Period after pregnancy

My period came like 5 weeks after giving birth and was pretty regular. I was supposed to start 2 weeks ago again and have yet to start and have no signs of starting soon. We did have unprotected sex the day my period ended and have since then been using condoms. I am not on any birth control. I have taken 2 pregnancy tests and both negative. This is my second child and if I’m remembering right I didn’t start my period after my first till he was like 3 months old. Is it normal to have a period then not have another for a while ? Any one else have this issue? Before getting pregnant I had regular periods and would basically start the same time every month.