Opinions Needed!

So I go sick with pneumonia for about a month all together and I couldn’t keep food down. Therefore, I wasn’t eating. I normally weighed around 115-120lbs. After I got sick I weighed 95 lbs. i’ve been trying to gain weight back but I’m barely gaining anything. I try to eat, like i’m hungry alllll the time but I can’t eat all my food ever because my appetite has gotten smaller. I also recent got on the nexplanon implant birth control, idk if that could have anything to do with gaining any weight back. But, I need some ideas, opinions, help?, etc. i’m 17