I've had dark brown semi formed diarrhea for the past 24 hours as well as nausea and pain in my lower left abdomen. I am having a cyst removed from my left ovary in a couple weeks. Should I be worried?

Any Health related problem is somewhat serious issue. It's better to consult a doctor and take precautions rather than waiting to get the problem even worse.

Call the doctor's office and tell the desk this. We can't possibly know if it is related or not.