We know condoms are a very effective way to prevent HIV infections. You used a condom for both oral and vaginal sex and they did not break, so I do not think you should be concerned that HIV is the cause of your Aphthae.
The activity you described has a very low risk for HIV transmission and so a negative test at 60 days is a very good indication that no infection happened. Testing 90 days after would be more for your own peace of mind and not because there is any real chance that the result would change.
Most people who are infected with HIV will have a positive test result 60 days after they are infected. It is very unlikely for that result to change if a follow up test is done at 90 days especially when, as in your case, the risk of transmission is so low.
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