Missed Period

My boyfriend and I had sex three times last month. Every time we used a spermicide condom and we were very safe. We made sure not to take any risks and he always pulled out. My period is late by 10 days and I don’t know what’s going on. There were never any tears and we didn’t do anything stupid. Im really nervous but I just don’t understand why it’s so late. I took a couple pregnancy tests and they all came out negative. I bought two different kinds and I did it properly and in the morning. Any advice??