When do I start testing?

I was on depo (this was the first shot so I wasnt on it long) and I'm due for the next one in the first week of August. But I wanna start ttc. I know it usually takes months after the shot to be able to start ovulating and be able to get pregnant. But last time (I had gotten the shot 3 times) i decided to stop getting it. I BD 4 days after my next shot was due never BD after that and 4 weeks later I found out I was pregnant with twins !!!!

So when should I start testing for ovulation this time ?