Ouch!
You know, I have genetic mess of a family myself. We've got a weird, slightly misaligned pair of neck vertebrae that can get inflamed and pinch a nerve that, so help me, loves to "mimic" things like heart attack symptoms among it's many other fun tricks. My brother and I (darkly, yes) joke, "How are we gonna tell if it's a real heart attack?"
(Actually, sometimes I wonder... don't dwell on it or anything but the thought pops up now and again)
I also was, over the years, involved in three rather serious car wrecks. None my fault. In fact, one, I was just the passenger when somebody tried to "beat" a light and hit my side of the car. So I get aches and pains (especially as I get older) that 99% of the time, I couldn't even begin to pin down what started which.
Meaning, it could be sheer coincidence that the muscle type aches started up the same time as vaping. And a back injury? Oh boy. Those love to mess with you. That's probably one of the main things that cause people to end up "hooked" on pain killers. A bad back can cause any number of crazy aches and pains. I got a second weird vertebrae that's not as bad as the family neck thing but there's this one stupid spot in my midback that when it gets upset at me, look out. The pain is never severe just relentless.
Anywho, that said, nicotine is a stimulant kind of thing. I've never had it do muscle aches with me but I've gotten "jittery" sometimes like too much coffee. And thinking about the coffee thing, times I've had too much caffeine, I do notice being more... aware (?) of aches and pains that I live with and usually ignore. Or maybe it's that being overstimulated makes muscles tighten up?
I could see too much of a stimulant making you achy.
Yeah, headaches and nausea are definite "back off the nicotine" signs.
One thing I'm starting to wonder (I'm not a "noob" so much now but I'm still pretty new... intermediate noob?

) is whether people who start (or I guess restart in your case) vaping don't pretty much inevitably "chain vape" at least at the beginning.
A couple of things seem to be going on. One is that the (most effective in nicotine absorption) inhale is different. And smoking is habitual. We have to shift long term habits. That can take a bit of time. The other is that the nicotine absorption is slower than cigs (which can get the stuff into your blood stream and to your brain in as little as 6 or 7 seconds according to studies I've seen) and that each puff may have less available nicotine than a "drag" on a cig.
Started thinking about this because I've seen a couple of conflicting studies out there. One, the researcher claimed vaping was a total fraud because nobody in his tests got any nicotine at all. But as I recall, he didn't have any experienced vapers. Just smokers he handed e-cigs to. At least one other study with experienced vapers showed the same level of nicotine in the blood as with smokers.
So that suggested to me that new (or newly restarted) vapers may have an adjustment period to hit their personal... oh... call it "sweet spot" of getting their nicotine. I know at the beginning, I vaped like a crazy person. Like I needed a way to just permanently attach the PV to my head and run a tube to my mouth.
And since I was a heavy smoker, I thought, "I should start about 24mg from what I've read".
Oooo. No. Bad idea.
(If nothing else, I gave myself "vaper's tongue" and that's just no fun at all!)
So I cut it in half, dropping back to 12mg. Now I'm starting to come back up with 18 and some 24. I vary it in fact. The flavors I really, really like, I'm keeping at 12. I tend to vape a lot of them just because I like them. I have some that are higher for times like when I just get up and have that "first cig of the day" urge or after eating (which was actually the harder of the two to break for me, something I didn't expect, I thought that morning cig would be the last to go).
Definitely try some lower nic. Maybe even nab a small sample of 6 or so. Also, something I found is you want to slow down in general. The absorption of the nic in vaping is in the mouth and nasal passages. And it's a slower absorption. As smokers, we all got used to getting the smoke in quick so the nic (among all the other chemicals they shove in cigs) hit the blood stream fast. With vaping, it's a more... relaxed thing. Find liquids you like to, oh, "savor". You know, spend more time with. Hold longer in the mouth because you enjoy the taste. That seems to improve the nic absorption of the puff.
Also, when it's a flavor you like, it's just gosh darn tasty!
(Okay, who wound Mark up this morning? He's being long winded again. Yeesh. I need an editor to cut my posts down or something.)