The only reason I think she might not be telling me is because since we've known each other since we were 13 and for some reason I've always been nervous/uncomfortable around kids, which she's well aware of, but lately she would talk about them and coo more than usual and make "awww, i want one" comments whenever we'd pass by a baby.
I really care for her, we've known each other for years and have been through a lot together as friends then in a relationship, so I really don't want to lose her. Although I never saw kids as part of the plan I care enough about her to make it work. I just don't know how to approach her about it? Or could she not be pregnant? I just don't know what reaction I’ll get so I’m feeling a little lost.
The symptoms you mention do point to a possible pregnancy. Mood swings, lower backaches, cramping without a period, and fatigue are all pregnancy symptoms. Having said that, she will have more information about her body than you do. She'll know for sure if she has had a period or missed one, for instance.
I'm female too so I know it can be kind of awkward to openly talk about worries that you might be pregnant when you don't want to be and especially if you know your boyfriend isn't ready to be a dad yet. If she is pregnant or suspects she is, she might just be really worried about how you will react! Why don't you ask her about it? Mention you have noticed some changes about her and you're wondering whether she could be pregnant. If she is, she will probably really appreciate it if you ask, so she doesn't have to worry about how to bring it up.