Having trouble staying wet.

Patient: I just recently had sex with my boyfriend of a year for the first time. We did use protection. I am 15 years old and we have now had sex three times. The most recent time it happened i found that after 20-25 minutes i was no longer, and could no longer become wet. I was still aroused and i was very well lubricated when we started. Is this a health problem? Is there anything i can do to prevent this embarrassing incident from reoccurring?