My Mum keeps asking "Are you sure you're gay"?

Hi all. I told my parents about 1.5 years ago that I was gay, and a few times she's asked me "Are you sure you're gay?" She's not religious or homophobic or anything, she was fairly cool when my sister decided she was gay.I'm 31, and I feel I'm gay. I've been intimate with 7 guys (not that she knows that!), dated 3 guys, watched a lot of gay p*** in the past, and basically feel gay. I don't understand women, I'm kindof scared of their parts, and I've only liked 1 or 2 before my puberty hit. Whereas when puberty hit, I basically thought about guys non-stop, even if I didn't really act on it.But when my mum asks me, it makes me doubt myself. I'm gay, but I've very subdued, quiet, I'm not a loud-and-proud out-gay man. I haven't even told my siblings yet. I have a long history of difficulty making decisions, flip-flopping, a regular Hamlet, never really being 100% sure on anything.I like guys, but I get a bit apprehensive about guy-parts. I get kindof embarrassed about sex, I've never felt totally comfortable talking about it or having it. I like the romance of a relationship, I just am having trouble adjusting to the sexual part. Maybe she's sensing that and that's why she's making me doubt myself?