I went for a trek and returned yesterday. I got bitten by leeches .I had fever for a few hours which soon subsided but now I am having Nausea and itchy sensation over the leech bite area.

Have you gone to see a doctor? Sounds like a infection or something that should be seen by a medical professional rather then a gaggle of internet dwellers.

Wouldn't be leeches unless you were trekking through swampy water. Hope it isn't a tick bite. If it is, it is probably still in your skin. Get to a doctor quickly! You don't want Lyme disease.