Yes, I would say stress or you are ill with something else, like Covid. You wouldn't get symptoms of an STD this quickly.
If it is covid (and I have no idea what the covid situation is where you live), you wouldn't have gotten it from her, either. Whatever it is, it didn't come from her. It's way too soon for you to see symptoms.
You used a condom for sex which is a barrier against std's. There is slight risk only and I mean slight. Skin to skin contact poses limited risk. If you develop actual symptoms of an std, then get tested. To me, you sound tired and stressed.