If i get infected by hiv, will my immune system be weakened in less than a month?

Yes: Very much so. During the acute illness, CD4 levels have dropped so low that quite a few people have gotten pneumocystis. Happily, they bounce back and hopefully the illness can be managed. Now why are you asking? I hope all's well. Your physician can help you if you're worried about having become infected, and I hope you'll be safe and not end up at risk.