Literally exactly the same situation mate. I was big in secondary school (18 stone too lol), lost a load of weight, got a gf of four years, split up before I started uni, didn't know how to be 'single' and what to do with this new found attention from girls etc. I think I'm probably a bit more confident than you and not so self conscious anymore, but I can relate to the club situation you talk about. I still don't go up to girls that I think are hot and chat them up, I have no idea why because I'm pretty good at holding a conversation and once I get going I don't have any problems. I guess I still feel they wouldn't be interested after years of reinforcement when I was younger lol.
Luckily I tend to get approached so that solves the problems sometimes, but its not always by girls I'm particularly interested in. I suppose you just have to man up really and get on with it. I'm getting better, but atm I just really cant be ****ed making any effort with girls!
Edit: At the end of the day (and its easier said than done, I'm a hypocrite), the worst its going to be is a no right? Yeah it's a little bit of a dent to the ego, but Brad Pitt would get a no too every now and then. If you can tease girls then just do that, and if you can dance then its probably better to get rid of the whole convrsation and get busy on the dancefloor.