Which pill are you on?
I found on Tri-cyclen Lo I was okay, I didn't gain or lose.
On Diane 35, I gained about 40lb... but my skin was aamaaaazing!! hahaha
Now I'm on the Evra patch. Honestly, when I miscarried a couple years back, I asked the doctor what the best birth control is for me, because I didn't want to get pregnant (was afraid of it happening again) so I didn't want to miss a pill...
And he suggested the patch. Now obviously I asked him if it would make me gain weight, and he said, honestly, you may actually lose some weight. But your boobs will get bigger.
Now the boobs didn't get bigger, but they stayed the same, and I'm able to lose weight.
I hope you can contact your doctor and see if there's a link between your recent weight gain and the pill, if there is, maybe ask him if he thinks the patch would be a better guess?