It can take up to 6 months for HIV antibodies to show up in a blood test, thus rushing off to your local medical professional, or to the local store to buy a home test kit, will not give you any useful information - unless you have exposed yourslef previously and have lareday sero-converted.
Assuming you travel often, I would suggest that when you are in the UK, US, or some other European country, you make a visit to one of the local STD Clinics for a test. These clinics are often found at hospitals.
You can usually take these tests anonymously, if only by dint of giving a false name, but you should also find some source of councelling to deal with the possibility of a positive result.
Aviation medical bodies have a varying views on pilots who are HIV positive, and so do many countries - many of whom will deny entry to those known to be HIV+. This included the US until recently, although I believe that this may have changed now.
I wish you the best of luck in the process.