changes after pregnancy

Hi! So three years ago I had my son. I was always on ADHD medication and anxiety meds, etc. After I’ve had him I’ve had trouble taking anything because everything affects me so strongly. My adhd medication now, after a year or two of not taking it for breastfeeding, I’ve had trouble with the same medication I was on for years! I’m highly sensitive to it even the lowest dose makes me nauseous and gives me heart palpitations. Has anyone else had issues with how your body processes medicine after having a baby?