Whatever the risks is for any particular type of exposure, of course it increases with the number of events. But when the risk is virtually zero anyway, it doesn't matter: double a near-zero risk is still near zero. There are no proved cases of HIV acquired by receiving oral sex, or by performing oral sex on women. If it occurs, it is too rare to measure or worry about, regardless of duration of exposure and with or without ejaculation.
1) About 90% of infected people will have positive tests by 26 days.
2) Given how low your risk was anyway, I do not recommend further testing. But if you remain unconvinced, have another test 6-8 weeks after the exposures.
3,5) The burning is unlikely to be due to an STD from the events you describe, unless you are having abnormal discharge from the penis. As to other possibilities, it's anybody's guess. Not knowing the cause, I cannot judge the risks to your partners. See a health care provider for examination and possible testing.
4) Most people do not lie when asked directly about HIV status, but of course there are exceptions. I'm not familiar with HIV frequency in Brazilian sex workers.
Good luck--- HHH, MD
Wow, are you a busy boy? Your sex is protected, so I would feel very reassured your not going to catch an std. You are acting sexually responsible. However, the doctor suggests you test once a year for stds/hiv if you are outside mutually monogomous relationships. Although 26 days is a little too soon to test by all medical standards, most people seroconvert within 21 days. They say 6 weeks is plenty of time and 3 months you are gaurunteed to be hiv negative. But since you practice safe sex, I would feel assured your hiv negative and will remain that way. Stay safe.