I took a fat burner pill (plastic pill) I feel like a lump behind my throat no pain swallowing at all but sometimes fell weak what could this be?

Something stuck. The pill may be stuck in your throat however, this is usually not the case. Often something irritates the throat when swallowed but still goes down. But it leaves the sensation that a lump is there. If there is something stuck it needs to be removed. See your local ENT doctor for an exam.