What are the signs of pregnancy?

I was on the Depo Shot and I recently missed my shot that was on February 23rd. My boyfriend and I want another child but are waiting and using protection and pulling out but we wouldn’t be upset if I were to get pregnant sooner. Anyways, my nipples started hurting March 20th and I thought maybe my bra since I was on a car ride? But it’s now been 3 days. Could I be pregnant? We have only done it maybe 3 times since my due date for shot was.