On valdoxan for 5 years, last 2 years only taking half a pill 12.5mg still makes me sleepy and tired all day. can i stop and use 5-htp?

Complex question: Valdoxan (agomelatine) is typically used as an antidepressant medication. 5-HTP is a serotonin precursor. I notice you also take lamotrigine. Have you considered the possibility that the lamotrigine causes tiredness? 5-HTP, in my view, is not robustly effective as an antidepressant. Bupropion (Wellbutrin) is unlikely to cause sedation. I would suggest talking w your doctor about alternatives.