I gained 20kg in 4 months, is duromine an option for me?

Need to examine: It is not feasible to provide a meaningful opinion without additional history, physical examination and may be some tests. Unless you overate grossly, on purpose, your weight gain warrants ruling out a metabolic/endocrine disorder. It would be prudent to see your doctor. You may start with a primary care provider so that s/he may determine if you need to see a specialist. Wish you good health!