Not sure when I ovulate...

Its been months since I had a normal period.. I had a miscarriage in April and got pregnant right away but miscarried again in June. I finally got a period about two weeks ago. I just bought some ovulation tests but have yet to test positive. According to this app, I ovulated Friday but when I took a test it read no and I’ve taken one every day since all to read no. I just want to know when to take the tests so that I can get close to my actual ovulation day. The app is telling me my next period is suppose to start in 13 days, but after going so long without one I can’t expect it to be a normal cycle. Does anyone have any tips?