The size of your tackle is determined more by genetics than anything else and despite what millions emails say, you can't really change the size of a penis (short of surgery).
The only method that successfully changes the size of a penis is those stretchy devices where a strap is put around the upper thigh and it attaches to the head and pulls it down all day. This method "works" in that the penis is indeed lengthened BUT it destroys the elastin and muscle structure so that you end up with a limp noodle that does not function properly. In some cases the lask of adequate circulation to the head kills off sensation.
No pill will enlarge a penis. A pill that has chemicals in it that force the blood pressure up (how Viagra basically works) will cause an erection, but other than being slightly more engorged than normal, it won't make any difference to the size overall.
The reason Viagra is expensive is that it is tested and has reliability - in gaining an erection, not in increasing size. I would discourage anybody from popping any pills in their mouth unless they are absolutely sure about what it is.
Speak to your GP if you are really interested in gaining in size - they've heard it all and a quick consultation will give you much better, proper medical advice than anywhere else.
Usually, females actually prefer a confident guy who has good technique rather than a racehorse. The average female organs aren't that large anyway, so if you had a massive penis, you either wouldn't get it all in or you'd hurt the lady.
Best bets? Get fit (or fitter, as the case may be), stop eating junk food and get out there and meet people. Everybody (and I mean EVERYBODY) has issues with some part of their body and it is the minority that are perfectly happy with how they look in their birthday suit, so may as well accept what you have and work out how best to make it work for you.