So I am taking Depo for the first time. I think I might be pregnant. Please help me understand if it normal.

So I am taking Depo for the first time. My first injection was on the 2th of September. My last period was on August 13. I haven't had my period since and I am a bit nervous that I could be pregnant. I have sex like 3 time a day and he always cums inside. We waited the 2 weeks they told us to wait but I am a regular on my period. To be honest I always had a stead cycle. We took a Ride Aid pregnancy test and came out negative. It just something feel weird inside me. It like i have cramps but I don't have a period. Can someone please help me.