I Get Sick To My Stomach After I Work Out Hard, Is This My Body Detoxing From Smoking?

When ever I go to the gym i sweat a lot and when I get back home my stomach starts hurting so i can’t really eat much which is bad because I’m trying to gain weight. I’ve been smoking marijuana for the past year everyday but I’m trying to quit, do you think my body is detoxing from the THC and thats what is upsetting my stomach? Also another thing I can’t eat much when I’m not high, its a kind of withdrawal symptom but my stomach doesn’t really hurt, only after I workout.