Dr. can't help so maybe someone can!

Alright so I've been spotting since the day after I ended my last period (4/2) and since I have super heavy periods and major cramps my doctor decided to have me only take my active BC pills then on my 4th pack take the placebo pills as well so that I get my period once every 3 months. We made this decision before the end of my last period so I hadn't actually skipped any yet. But since the end of my last period, April 2nd I've been spotting nonstop and she decided to switch me to a different pill. after switching it finally stopped and my boyfriend and I decided to have sex sibxe it had been a while and it was finally gone but the day after I started bleeding super heavy and it's like I'm on my period with a super heavy flow. I've also been having awful back pain since the spotting started in April that won't go away. anyone have any idea of what's going on? my doctor is at a loss and doesn't know what to do.