I've been taking 200mg once a day of 5-htp for three weeks and been feeling extremely sore after working out , will this stop once i stop taking 5htp?

One way to find out: This is not a typical side effect so it may have nothing to do with the 5-HTP and merely be a coincidence. The only way to find out is to stop it and see what happens. If it stops then start it again to see if there is cause and effect. In 1989 a batch of tryptophan was contaminated and caused muscle pain, but this has not happened since and not been reported with 5-HTP.

Eosinophilic myalgia: Eosinophilia–myalgia syndrome (EMS) is an incurable & sometimes fatal flu-like neurological condition linked to the ingestion of L-tryptophan. While 5-hydroxytryptophan (5-HTP) is a metabolite of L-tryptophan (& therefore different), the causative metabolite / contaminant was never found or proven. (Suspicion falls on "peak AAA" but no one knows what that is or if 5-HTP has it). Best to avoid.