Is it safe to take melatonin with lexapro, buspar (buspirone) and ramipril?

Melatonin: Yes. Of course. This commonly used herb is a very safe addition to complicated medical and medication issues.

It would be best to discuss this with your Psychiatrist. If you are not confident with your Doctor see another for a second opinion. It's good to have a physical exam to rule out illness. Sleep is very important for physical and mental health. You may need a sleep study to determine why you can't sleep. Also consult with a Clinical Psychologist with expertise in multiple types of psychotherapy.