I’m positive for chlamydia

Im currently 24weeks pregnant with my 3rd baby I’ve tested twice once at my first hospital visit and the other at the doctors both show positive results my partner has tested negative twice I’ve been with him for over 10years he’s the only person I’ve been with and he said he’s never cheated on me but how could I possibly test positive with no other sexual contact or partner? Could I have caught this on my own ? My last pregnancy was 3 years ago with no diagnosis of me having this disease ? Is there any other ways it can be transmitted to me or could he have carried the disease over 10 years ago before we dated or is it just a case of dishonesty and cheating??