Are you on an antidepressant?

When your mood is good, you want to exercise and eat healthy, which makes you happier and the cycle goes around like that. If your mood is bad, you want to feel better which manifests itself as impulsive and self harming behaviour.

When stopping an antipsychotic, it's likelier that you'd have more negative thoughts about weight, have overactive thinking, delusions.

Try the metformin (My dad is on this and has lost weight but stopped taking and gained the weight back).