Should i be concerned about stds/stis or hiv?

Depends.: If you share or plan to share bodily fluids (inc. sex toys or needles, some rare instances of medical procedures) with another person or use IV drugs, or have done so before, then you should be concerned about STD's, inc. HIV. If you never have, don't now, and are never going to do those things, then you don't have to worry, generally speaking. Pretty impossible! So be smart & safe.

Yes: we should all be concerned and careful if we are sexually active with more than one partner

Yes: Please forgive my frankness. You're almost a grown man. Many of the things that adults have told you in the past are not true. However, there really are diseases that can damage or even kill you that you get from having unsafe sex. Even if you have no regard for your own life and health, you should consider the risk of transmitting something to a partner.

Definitely: If there is suspicion of having STI or HIV or there are risk factors for acquiring STI which include multiple sexual partners, unprotected sex, Iv drug use , prostitution, men having sex with men, previous STI then consulting a physician or sexual health clinic and getting appropriate test is very important .