PLEASE HELP! TMI WARNING

So my doctor started me back on BC (low dose pill) to treat severe pain I get from cycsts. I've now been on it for three weeks, I've had two periods. The first was 6 days and the second (which I'm still on) has been going on for 12 days now. I have also developed a yeast infection I believe is due to the long term bleeding and it is extremely painful now to use tampons. Should I be worried or is this something that can happen when starting birth control? Any help would be greatly appreciated, I feel awful. 😖