Welcome. Thanks for your question and for the thanks about the forum.
You had protected sex. Although in theory an open penile sore could increase the risk, the odds are your partner didn't have HIV and condoms work. As for your symptoms, they include some aspects consistent with a new HIV infection, but also with many, many other conditions that are much more common. Other symptoms are not consistent with ARS, notably diarrhea is not a usual feature (although it can happen); and absence of fever is strong evidence against ARS. Finally, the timing is late, since ARS symptoms typically start 7-14 days after exposure.
And as you suspect, your negative HIV antibody test 4 weeks after exposure is highly reassuring. Time since onset of symptoms is less meaningful than time since exposure -- but in any case over 95% of the time antibody is detectable within 30 days, and within 10 days of onset of symptoms. (In fact, it is appearance of antibody that is partly reponsible for some of the symptoms of ARS.)
Standard advice from many authorities suggests antibody testing at 3 months for fial reassurance. Six to 8 weeks is actually sufficient, but 4 weeks is a bit short. Alternatively, find a doctor or clinic that offers the "combo" or "duo" test for both HIV antibody and p24 antigen. That test is 100% reliable any time after 4 weeks.
If you decide on further testing, stay relaxed in the meantime. It is exceedingly unlikely you have HIV and you can expect future test results to remain negative.
I hope this helps. Best regards-- HHH, MD