Good Enough Reason To Change Pill??

I started off on Loestrin 20 (as a side note, how's that pronounced?? So when I tell my doctor I don't sound stupid!!). I'm now on Marvelon, because I was getting breakthrough bleeding.

I haven't had sex in nearly a year, it's not for contraceptive reasons I'm on it! I used to have really irregular periods, and really heavy ones. Now the problem is, on Marvelon, my periods have gone back to being quite heavy again. (I use a mooncup, and over night I can wake up to have blood EVERYWHERE because its overflowed by that much. This tends to happen 4 out of 5 times!!). Can I ask to change pills to help lighten them? Is it likely that there will be a pill available that will lighten them, also avoiding the issues of breakthrough bleeding?? And also.. What causes breakthrough bleeding?? I was on the first pill about 6 months before it started happening.