i thought coming out was hard..

I don't think it's that she doesn't support you. It's probably a combination of two things.

There was an article sometime back in NY Times or somewhere talking about how there are an awful lot of people that are open and accepting and embracing of gay/lesbian people, but when it comes to THEIR son or daughter, their response is different or more challenging. And in the analysis, it basically boiled down to being willing to accept the "loss" of a "normal" aspects of having a child, since regardless of how one looks at it, being gay or lesbian is still different, and viewed differently, than being straight. So I suspect that part of it is just learning to adjust. It's not that she doesn't support you or doesn't love you, it's more about coming to terms with something that's pretty different than what she probably expected for 16 years.

The second part is I think that for most parents, any discussion relating to sexual activity, but particularly to gay sex, with a son or daughter is probably rather awkward. In part because for most people of your parents generation, there's still some sort of deep-seated discomfort with being completely open about things related to sex, and in part because talking to your child about sexual things is also acknowledging that your child is growing up... and that in itself can be a challenge.

I'd just give it some time, and maybe, depending on your relationship, directly talk about it, gently saying something like "I'd really like to discuss this, because I think it's important to our conversation and openness. I feel like when I discuss things related to my being gay, that it makes you uncomfortable, and I realize it's probably difficult to even talk about this, but I would appreciate it if you could try, because I think we can get past it and it will make our communications better." I think if you do that, she may well be willing to at least try, and both of you might come away having learned a lot about yourselves and about each other.