Advice needed!

Hi! I am a 22 years old and have been on birth control consistently for 4 years now (for almost 2 years now, I've been on Mya). I have tried birth control with higher estrogen, higher progestrin, a combo pill.... Nothing has seemed to improve my periods. My symptoms are extremely irregular periods. For example, sometime I will bleed during the period week of my birth control, stop for a week and then bleed for another 2 weeks during the middle of my birth control pack. (I take them the same time every day, never missing a pill). Sometimes I bleed for a month straight and then skip a month. Usually it's a lot of dark spotting, sometimes it's moderate-heavy bright red. I have a lot of large blood clots. 1" in diameter and at least 2" long, always very stringy. Naturally I'm kind of concerned so I spoke to my family doctor and went to a gynecologist. I was really positive and hopeful they'd find a solution for me. They took bloodwork and gave me an ultrasound and nothing turned up wrong with me. The only suggestion she gave me was to get an IUD instead of birth control. I'm a little wary of IUDs so I plan on staying on birth control. Has anyone had a similar experience? Is it just birth control? Could they have missed something? Please help, I'm so sick of cramping and bleeding for the majority of every month.