Period talk

So around last month, before my 18th birthday which was July 21'st I had gotten on birth control. The shot, (demo)  I waited over 7 days to become sexually active again, even with birth control, pull out method was used. Its August now and my period hasn't came...I took a prego test and it came out negative. Can someone tell me if this is normal and I will be expecting my period!? Because eve has been telling me my period is 26 days late!