Weird symptoms

So I had sex about 14 days ago. Protected sex, for five minutes with a condom and he didn't ejaculate, there were no breaks.
I got my period when I was supposed to but it was very light, but lasted for five days with bright red blood.
Now it's after my period and I'm still scared of pregnancy
I took a test 19 dpo and it was a clear negative, showed up quickly and no faint lines
I've been very stressed lately and I'm still having symptoms after my period, like full boobs (not sore), a little backache, hot flashes, and stomach ache.
Is this all in my head and from stress? Or is it hormones?