Is it std? Late period :/

I had sex almost two weeks ago with my so called ex now. I have been having yellow discharge but not green in colour. From what I have read, symptoms of std’s discharge is yellowish green. But i only have yellow discharge. Can anyone tell me more about this whether to see doctor or not. I honestly dun feel the need to as I am not experiencing any other symptoms of having std.

My period has been late for 27 days but keep having pre-symptoms throughout.. I have also taken a pregnancy test reading I’m not pregnant.

Any ideas/advices or suggestions? Help this girl out :(