http://www.t-nation.com/free_online_article/most_recent/12_programs_to_follow
Pick between 1-5 (full body, push/pull/legs, superset, upper/lower) lift 3 days a week and swim. Eat for your goals... swimming and lifting require high carb but don't neglect protein.
The "v" comes from a wide back, developed shoulders/rear delts and a narrow waist. I wouldn't neglect legs because you do use your legs for swimming to an extent unless you're doing like a triathlon in which case you conserve your leg energy for the running/cycling.
Stick to a routine and eat properly.
And if you are dead set on running a ph at 18-19, you better do it right. Like other and myself have already said, you're young and you are under 150lbs, you can put on 10-15lbs EASY in like 6 months. If you run a cycle for say 4 weeks, you'll gain 8-10 and then lose a few during PCT so in 8 weeks (cycle plus PCT) you'll gain 6lbs or so. This can be done naturally in 8 weeks. Sure, you may only put on 4-5lbs of lean mass in 8 weeks as opposed to the 6 in this hypothetical scenario.
BUT!! By running a ph you'll mess with your hormones which are probably already running efficiently. Your biggest issue is you don't eat right, running a cycle won't magically put on muscle/size/mass if you don't eat the carbs/protein/fats necessary to put the damn shit to use.
I am in no way trying to bash you, simply educate.
/thread