Hmmm?? Advice

I have been off of birth control ( nexplanon ) for exactly 4 weeks Tuesday and have not had a single sign of a period yet. Also did not have a period while on the birth control. I am TTC and have been since I got it removed. Question is how do I know when I have or haven't ovulated or conceived? Since I haven't had no period.

I have been taking ovulation tests and pregnancy test for the past few weeks. They have all been negative.

I want my babies close in age My son is now 7months.