How to know if you have an std from giving a bj?

I gave a bj to my new partner Friday night. I’ve noticed today that at my gum by my one tooth is kinda sore and there is a white spot. But I’ve also used those disposable mini one time use plastic tooth brushes and not sure if it’s from that. I do kinda remember hurting my gums using them but don’t remember if it was at that spot. My new partner was just tested for stds before we ever did anything and came back negative.

I was tested as well beforehand and also tested negative