Hello
Oral and  anal sex , unprotected sex .
Red bump around groin area , just after 3 days of exposure , it is very difficult to say , that this bump is due to 
HIV or not . 
Antibodies to HIV begin to appear  within 2 weeks of  primary infection .
Approximately 50-70 % of infected individuals experience  an acute syndrome following primary infection . The acute syndrome follows infection by 3-6 weeks ( in your case this bump is just after 3 days , so questionable ?).
There is a  strong association of transmission of HIV with receptive anal intercourse, probably because only a thin , fragile rectal mucosal membrane separates the deposited semen from potentially  susceptible cells in and beneath the mucosa and trauma may be associated with anal intercourse.Anal douching and sexual practices  that traumatized the rectal mucosa also increase the likelihood of HIV infection .
So , you are at higher risk case ,so get in rapid nucleic acid amplification test ( P 24 pcr , 
rna ) . 
The groin bump may be due to bacterial infection so take 
azithromycin +
levofloxacin combination  for 5 days .
As I mentioned above get in this test after 2-3 weeks of initial primary infection.