I think a lot depends on the type of PV you use too. I've been vaping for about 2 months now (was a 20 a day smoker). I started out with an eGo cartomiser kit with 18mg juice, which did the trick perfectly for the the first week or so till I ran out of juice. I ordered some 14mg juice as part of my aim was to slowly reduce my dependency on nicotine. I found that the 14mg juice worked, but it took me a couple of weeks to adjust to the lower nic level. Then something very bizarre occured, I bought a lavatube and some 306 atomisers for direct dripping. Wow. All of a sudden the 14mg juice was giving me really bad ringing in my ears and I was struggling to relax at night when trying to go to sleep. Since then I have started to mix my own juice. I'm still dripping with 306s, and mainly vape 8mg (which does absolutely nothing for me in a carto by the way). I also carry a bottle of 16mg which I use quite a lot at work when I don't get the chance to vape as often. I keep well away from the stronger juice in the evenings if I am relaxing at home, although if I am going out drinking then I find I need to use a stronger juice to keep the alcohol assisted cravings at bay.
Sorry to ramble, but I guess what I'm getting at is that there are so many variables involved with vaping that judging what strength juice you need is a very tricky affair. It has taken me two months to figure out what I need. So in response to the OP, get back on the vaping (especially if you have been back on the smokes for 3 weeks) but be prepared to make adjustments in strength as and when you need to.