Guys, thanks for all the replies, really helpful.  I'm not exactly new to BB, I've always barebacked with my 4+ years BF, but initially I was on the bottom side.  In the last couple of years I've been more on the top side and we've been piggies (3 somes, sex parties, cum dumps) and I started being more bothered by this problem.  
Jerking off: I noticed it too.  If I don't cum in a couple of days, I don't last at all.  I'll try to jerk more often when I'm piggie :-) 
Multiple cums: I wish, but never happened.  As I said, I noticed that several times I stay hard after cumming, but my interest in fucking the sloppy ass goes down (maybe because I get frustrated that I already unloaded).   I will try to keep fucking next time! 
Sex pills, like the ones you can find at theses stores here in SF (e.g. Lightning rod): I tried them a couple of times, different brands.  They seem to work, but I'm not sure if it's just a placebo.  Any thoughts on them? 
Finally, I think I just need to have more sex and fuck more willing bottoms here in SF