What do you think? I'm worried!

Cycle length is usually right at 29 days. I'm on birth control and we use condoms, so double duty... but my cycle is 5 days late. We only did 2 times in the last month (busy) and both times were double duty. The last month was stressful, and I took a test yesterday that came up negative. I don't have any symptoms except back pain, but I've had to move classrooms and am now sitting a lot that the school year is done.

We're getting married in 7 months and I can't afford to get pregnant at this point!!