Confused about my weight... :|?

Okay so im 5'5 about.. Before christmas break i weighed lke 100 and now i weigh like 105. I know it doesnt seem like a huge deal;; but i cant fit into my favorite jeans anymore and pretty much all my jeans? :( it just makes me depressed cause when i look at myself in the mirror i almost cry.. ;; like my mom said i should get up to 120 and i know girls that weigh about that and look gorgeous.. but i want to stay at 100 and considered going anorexic about it;; and then my moms like "if you even think about droping a pound im bringing u into the hospital and telling the doctor you need pills to gain weight" or whatever.. its like wow im not even that skinny o.o.. and i've been wearing sweatpants for school for a while and i told my friends about my problem and they just asked if they could have my jeans and crap. It's just like they dont even understand? So i need advicee..? Please no rude comments :|