Most things have been covered here Marc, Bumrungrad Hospital is well respected but the Red Cross hospital near Silom do HIV consultations if you do have any problems whilst in Bangkok. I would not mention your HIV status to any Thai Embassy's as each Embassy can react accordingly to their own rules. As a positive person I would think that you are already immunized against Hep A and B (which is always a good idea for any travelers to Thailand) and a flu vaccine would not go amiss either. Your doctor will advise you on these.
Medications, carrying enough plus a safety margin will be good, but I would have the pills in an open prescription bottle depending how many you are carrying and also have a copy of your doctors prescription just in case you are stopped and an over zealous customs guy wants to know what your drugs are. Like Smiles I have been traveling to Thailand since 1987 and have never been stopped going through the 'Green' but one never knows.
Have a safe trip and enjoy.