You wrote:"Tests: Got tested on 20th April’07 (10 weeks after last contact) for HIV using ELFA – VIDAS method ; result – negative (it says 0.03; > 0.25 is positive, <0.25 is negative). Got tested for Syphilis twice (20th Apr & 29th Apr) using TPHA method; result: indeterminate both times. Doctor advised 2.4 mg Penicillin injection which I had. Moreover, would getting a penicillin injection for possible syphilis mask my chances of HIV antibodies detection in future? I had a penicillin injection on 29th April'07"

Given your description of the sexual contact you've experienced, it seems that you've participated in risky behavior. If the girls had HIV/AIDS or some other STD, you could be infected. The HIV-test is negative for now but due to the disease's incubation “window period” you SHOULD take another test after 3 months. Penicillin can't interfere with antibody detection. And rest your mind that regardless of which “common HIV-related symptoms” you seem to be experiencing at the moment, the HIV-test will be positive if, indeed, you have contracted the disease..