Hello. I Am In A Long Term Relationship (3 Years)

Hello. I am in a long term relationship (3 years) and I had recently had a swab comeback positive for the std Trichomoniasis. I was told my previous swab was negative . I know all previous swabs were self taken by myself in the toilet while the positive one was taken during a smear test. Is there any chance the previous swabs taken by myself were not correctly taken or good enough and have missed the infection or the infection was not predominant enough or has my partner cheated on me with an infected person since my last swabs or is it catchable any other way than sexual inter corse, Thanks