Help.....

I've been trying to get pregnant for almost 6 months now. I have ovarian cysts and endometriosis so if I am off of my BC too long the endometriosis can come back... I'm terrified of that happening. I am now taking chlomid to force me to ovulate and am about to start my third month of the drug. I have taken ovulation test the past 3 months and not once have the test shown I was ovulating. I thought it was maybe the time of day I was taking it but I switched it up each month. Last month I got a positive pregnancy test and two days later it was negative. I don't know if I am doing something wrong. Anyone have any suggestions or ideas as to what is going on?