Should I be alarmed or is this normal for my age?

Anonymous
I'm 17 years old and I have always been pretty thin... the highest my weight has ever been is 130 and I'm 5"6... However this semester of school I started losing weight and it wasn't intentional... I've lost a total of 20 lbs. in this entire semester, which means I only weigh 105 lbs. now...

I know some girls when they reach a certain part of puberty/development they lose weight, but is this much weight in this amount of time normal?
Updates
+1 y
I've had health problems in the past (heart problems), and if I bring this to my doctor he will do a very drawn out investigation into everything and I don't want to go through that again if I absolutely don't have to...
Should I be alarmed or is this normal for my age?
7 Opinion