First time actually ttc

So I'm so new to this. But I lost my babies recently. And dr said I can try again. But I was so hurt (it was my first loss it was twins) so I told him I wanted the BC shot. When I got pregnant with the twins I was just 4 days past the day I was supposed to get my 3rd shot. So I instantly was able to get pregnant for some reason.

Well this time it was only 1 shot. And I'm wondering if maybe I can get pregnant again ?? How long would it take to start ovulating. Can I start testing my ovulation.

(Period wise I'm so irregular it's crazy so I don't know when to test)