TTC in sept!

I only had 2 shots: Sept 18 at 6w pp appointment, Dec 10. It took 2 years to conceive #2 and we thought she was the last so I went on the depo (first birth control ever).

I was supposed to get my last shot in mid March (March 11ish) but stopped due to bad side effects. I had only two 6 week periods about 4 days apart (instead of steady 3 weeks and 2 weeks apart). I felt a very small cyst on my ovary yesterday which was normal before birth control.

My question is. How long until fertility comes back. How will I know? We want to TTC in september and I'm terrified to go thorough more infertility....