You bet it can, and you're right thinking that the bc pill is the culprit. Which brand are you using?
Ortho-tricyclen, ortho novum 1/35, and cyclessa are all known to put on weight.. Usually around 10-15lb.. Although side effects vary, some girls break out in acne, some have stomach pains, and some suffer no problems at all. Otc (ortho-tricyclen) is also known for making a considerable increase in breast size, much of time without an increase in weight anywhere else in the body.
Nuvaring has the lowest hormone levels, so you suffer less side effects and less weight gain as a result.
Also note that ovcon actually markets their product as being able to keep weight gain under control, and many women have confirmed they have gained little to no weight on ovcon.
My recommendation: if you'd like to increase your cup size a bit, try out otc and see how your body reacts. If you find you're gaining unwanted weight elsewhere then after your cycle is done, you can try switching to nuvaring or ovcon.
I hope this helps,
justin