Im no doctor, but I am in Nursing...and I used to work for a local OB/GYN's office, so I thought I would try to help....

Prob the reason it is affecting your cycle is Estrogen is stored in fat cells. Produced in your ovaries, the hormone cant just circulate and be eliminated in your blood stream....your body stores it in your fat cells so there is a ready supply....thus the reason why women with less than 5%body fat have no cycles...they have no estrogen stores...and also the reason why it is more common for women with high body fat to be more prone to cycle problems...that being said....the pill (depending on which one you are on) helps to regulate that by providing a daily intake of estrogen/progesterone....however, if your body is 'digesting' or metabolizing fat stores, you may be releasing more estrogen into your blood stream, putting too MUCH estrogen circulating, causing the bleeding problems....you may just need a BCP with a smaller amount of estrogen in it while you are LCing....

Again, NOT a doctor....but learned the above info from a FABULOUS OB/GYN I worked for...talk to a local OB/GYN...I hope this helps....Good luck!!!

If I can help answer any questions....drop me a line....