Irregular Periods and Heavy Bleeding: What's Going On?

I have periods extremely irregular I have since my first one at 12 at first I was regular 2 months then I have 3 a month for a year then I skipped 3yrs and went to having them once every 3 months now it skips years and months and is all over the place, my doctor's know and never said anything like it's normal till recently my knew doctor told me that it's not normal any idea what would cause that? I do bleed heavier than average when I am on my period it lasts 1-2 weeks and I bleed enough I use night time pads and have to change every 1-2 hours and double at night, I also get very nauseous and have trouble walking I'm assuming from blood loss. I tried birth control but it stopped my periods completely sometimes and so I tried another type and it made them way to frequently like more than 1 a month less than a few days apart