I am 19 years old and am taking Tri-Sprintec birth control and have been since March of this year. I haven't missed a pill until today and that's because I dropped it down the sink. I'm not sure what to do since I completely lost the pill.

This says that you take the "next" pill the following day, resume the cycle and use another form of birth control with Tri-Sprintec for two months. Tri-Sprintec Facts and Comparisons at Drugs.com