Hello. So I Had A Pelvic Exam 7/20/16 On 8/24/16

Hello. So I had a pelvic exam 7/20/16 on 8/24/16 it came positive for trich STI my only sex partner in the last 2 years went to get tested and results were negative for any STD and STI. during the time of me getting tested and getting results me and my partner had unprotected sex multiple times and he has not had sexual relations with no one but me. Is there any other way I could have contracted this STI? And What ways can it be contracted ?