I'm going to skip personal experience and cut straight to advice..
Don't worry. There is no reason you would know about your own sex drive until you've had experiences which help you navigate it. Or, more accurately, there are lots of other emotions which are going to get in the way, so give yourself time to relax and become comfortable.
To take an example, as an adult I'd presume you don't sit around and pretend you're driving a car because it wouldn't feel realistic. Any emotion or thrill you got from driving a car could only be experienced if you'd actually driven a car and could remember doing it. We can sometimes simulate it a little by fantasizing, and that's why porn exists, but ultimately noone knows their sex drive until they start actively testing it through sexual experience.
If/when you start having sexual experiences, you'll probably discover things which you like and things which you don't like. The things which you like you'll remember, and sometimes you'll remember them and it will be hot. That's a sex drive.. it's something you build up through experience and active fantasy, not something which is just there.
Erections are meaningless, especially in adolescence. It's just a purely physiological response which doesn't necessarily have any sexual component at all. Some people will get them a lot and some people won't get them at all, it means nothing either way.
Don't rule yourself out as asexual. Some people genuinely are asexual, but don't let yourself get labelled for no good reason. Sexual desire won't just fall into your lap (heh), you have to take the time to fathom it out. Those little brats who are horny all the damn time have just been sexualized early. Probably by jacking off to too much porn.