Can tonsils be the reason why i dont gain weight?

Im 20 and my weight is stuck at 39kgs since the age of 16. Back then i used to be 5'2... and now im 5'6. I eat healthy but im still unable to gain weight. I eat just as much as my sister does who is 1.5 years older than me... she can easily put on weight. I think i have tonsils... i can feel these bumps in my throat. They're not painful though. If i get them removed will i be able to gain weight? I have a serious problem with my weight. Recently i was on anti depressants which make you gain alot of weight... around 6 or 7 kgs... but i could only gain 1kg. One week back i discontinued the pills and lost that one kg i had gained.