fatherdano, when I get heartburn, I drop my nicotine. I've gone from 24 to 18 to 15-16 to (now) about 12 over the past 2-1/2 years....and heartburn was my strongest indicator. That's just me, but I'd try some 12-15 mg nic and see if that helps. Also, I've always heard headaches meant too much nic and/or not enough water. Are you drinking LOTS of water? (More than you'd think you needed, I mean.)
That dull headache also tells me I'm not getting my caffeine. When I first started vaping, coffee flavors were among my favorite tastes, and I noticed I was getting that dull headache and realized that I was drinking WaaaaaaY less coffee than usual. Once I got back to my coffee (and dropped the coffee flavored juices for fruit flavors, mostly) the headaches went away. Couple of things to think about.
That said, I can't BELIEVE you've been at this for 5 weeks already! Where does the time go???!!! It seems like you were at about 7 days last I tuned in! You really are the poster child for new vapers in my books! You already seem like such an "old pro"....and I don't mean that "old" in the sense of "old."