How shud u go about fasting if your on meds (pentasa (mesalamine) mesalazine, sertraline and risperidone), can i still take all of these while not eating for 7 days?

No: Never a good idea not to eat especially for 7 days whether on meds or not. Evidence shows that the best way to lose weight is to decrease portion size and not skip meals. Also, never stop taking any prescribed meds without talking to the doctor who prescribed them.

Medication should be managed by your Psychiatrist. It's a good idea to have a complete physical exam to know if you have a physical illness that is causing problems and how you should approach your eating schedule. Your problems could be helped by a Clinical Psychologist with expertise in multiple types of psychotherapy. If you are not confident in your Doctor see another for a second opinion.