If you got an infection due to using dirty needles, old cottons, a solution that was left at room temperature, or any kind of dirty/old equipment you really should get checked out as soon as possible. Waiting too long could be the difference between life and death.
People often get overconfident when it comes to shooting drugs, I've seen all sorts of ridiculous claims on this forum (thankfully they usually get corrected by someone else).
One needs to be as sterile as possible every single time, remember that bacteria and other microorganisms are invisible to the human eye, you don't know what might be growing in there (and there will be something growing, the only question is whether your body will be able to deal with it).
Otherwise it'll be like playing russian roulette... And there are way worse outcomes than "cotton fever", endocarditis is one example.