I am 35 years old. Had my period on 6th of June, though the flow was not my usual flow. Have started spotting last 2-3days. Also feeling very nauseated & feverish all the time since last one & half weeks. What could be the reason? I never had such irregular spotting ever in my life.

You need to talk to your doctor. It's the nausea and fever that worries me the most.

If you use tampons, it might be TSS.