Do I have chlamydia or maybe just irritated?

Patient: I think my boyfriend may have cheated but am uncertain. I was having symptoms of Chlamydia but tested negative. I took the antibiotics anyway however and my symptoms went away. Then we were intimate again two days ago, and my symptoms came back but seem worse. Is it likely I have Chlamydia and just tested negative? It seems odd that I would test negative, take the antibiotics and then have sex again and get similar symptoms. Or could it be something else?

Symptoms: Lower abdominal pain (mild), lower back pain (mild), some anal itching (mild)