Is it normal to think my friend is pregnant?

I'm sorry that I wouldn't vote because I really can't tell if she's pregnant. But from the signs that you've observed so far, it's really very possible that she is.

No matter she is pregnant or facing other problems, as her close friend, I think you should show your care to her. I know how awkward it can be to ask her questions or just talk to her about her problems face to face. But it's not necessary to have a conversation because there may be things that your friend doesn't feel comfortable talking about or she would need some time to think about how to tell you her problems.

So my suggestion is that you may write her a letter or a card saying that you're worried about her and telling her that you'd always be there for her whenever she needs you. And in the letter/card, you may as well encourage her to open up to you. After all, it's her decision whether she wants to tell you her problem or not. What you can do is to wait for response and keep observing.

We're looking at a major variety of factors here.

If she's pregnant, then she probably got pregnant, told her boyfriend and he decided to get out of dodge and broke up with her and she is now looking at the prospect of being a single, teenage mother and watching her whole life... college, finding a great husband, having fun with her friends, parties, getting that awesome sports car... just slip away. That'd be enough to make anyone depressed.

No matter how much you support her, nothing you can do will ever change the fact that her quality of life in the future will be forever compromised unless she gets Anna Nicole Smith lucky. But then again... she's dead now.

Or, the breakup caused a switch to flip her into depression and the weight gain is from her metabolism slowing in response to the lack of happy activity compiled with her eating which may or may not have been excessive in the first place but was eaily handled by her quick, active, non-depressed metabolism.

She could have been raped, abused etc. and not necessarily by her boyfriend. Such a change in behavior could be a reaction to the breakup(active hormones make EVERYTHING more intense then it really is), but then again, it could be a lot worse than it looks.

Either way, you're probably going to want to find out what's wrong. Depression, isolation, weight gain, if you have ever been forced to sit through a sex-ed class lesson about the warning signs of suicide in high school, you'd know by now that those are among the first warning signs. Srsly.

thank you for your comments.
NeuroNeptunian i don't think she has been raped or abused,for i think i woud be able to tell (it happend to one of my friends a few years ago),your suiside theory worrys me, but it's a bit hard to tell we don't have sex-ed classes or anything like that were i live.
thanks again of your advice.

It's hard to tell.

Tell her how you feel and let her know you'll support her no matter what.