Why is my period late

I am not sure if I am pregnant or not. My period is five days late and I'm beginning to get worried. My boyfriend and I have sex mostly with condoms and he has definitely never came inside of me when we weren't. We use condoms with spermicide too. Lately I've been a bit stressed and even more so now that I am late. I've also changed my diet and I have been eating a lot less. I know that those could influence my period. The last time we had sex was 10 days ago and we have always used a condom when I was in my fertile window. What do you guys think?