Helo, what do you recommend for weight gain?

Please have your doc do a checkup to rule out a medical problem. Then consider visiting a nutritionist to see if some simple changes in your diet could add high caloric density foods to replace lesser ones. Also consult with a trainer to design a program of resistance training that would add muscle mass rather than simple fat stores. Simply eating more may just add fat- not a good plan.

How much do you weight and how tall are you? If you are otherwise healthy but just skinny, do not be concerned. With age you will gain weight and look at this time fondly when you could eat and not get fat. For healthy diet: http://www.choosemyplate.gov/ Get HPV vaccine. Wish you good health! Safe sex: https://www.hopkinsmedicine.org/health/wellness-and-prevention/safer-sex-guidelines