Receiving unprotected oral from a female on the penis is in general low risk. Possiblities are HPV (not well studied) HSV, gono, NGU, and syphillis. Without any obvious lesions your chances are slim. HSV can shed with no symptoms but transmission odds are pretty low in your exposure. If there was lots of deep throating bacterial transmission can occur. NGU probably being the highest risk.
With no symptoms you most likely have no STD’s from this exposure but it might be a good idea to start having routine tests to ensure safe sexual health
Not immediately no test shows results immediately.THERe is window period. Ask the testing centre the window period for which std you wanna get tested and they will guide you.