Jealousy is taking over me?

I feel like I'm insane. I have been feeling this way for about half a year now. I have been getting jealous at my friends a lot lately. I used to be jealous when they go somewhere without me, or take pictures without me. And I'm scared that they will ditch me or something like that. But that's not the case anymore. I get jealous simply when they talk and I'm not included in the conversation, when they are both online on Facebook and commenting on each others' pictures or status, or even when they take pictures and I'm not in it. I want to know what they are talking about, or what they are doing. Sometimes I would do things with only one of them, and I don't see a problem with it. But I get very jealous when they do something without me. I didn't tell them any of this and I'm not going to.
I'm up to the point where I'm so insecure that I will lose them, or that they don't want to be my friend. I'm even crazy enough to think that I need to stop my friends from going on Facebook so that they can't ***** about me online. And also, I feel very excluded. Like they talk, take pictures, hang out and all that without me. But I never go up to them, I expect them to come up to me. I know it's wrong, but I don't want to look pathetic and try so hard to be part of the group when they are excluding me. I try to seek attention by laughing at something on my phone and wanting them to ask me what is it and all that. But I know it's stupid. I know there is not point, but I can't help myself