The only way to find out is to test!
HIV may not cause any symptoms for several years, and there are no exact symptoms for HIV. 2-4 weeks after HIV infection, you MAY get flu-like symptoms like fever, headache, rash, and enlarged lymph nodes. Years after infection with HIV and no treatment will weaken the immune system and put you at risk of TB, certain chest infections, fungal infections etc.
These illnesses aren't only due to HIV, so if you think you've been at risk of HIV infection within the past few weeks, you should get an HIV test. While living with HIV does not immediately cause symptoms, the virus continues to be active and causes progressive damage to your immune system. This is what makes it so important to know your status.