Honestly.... I know there are plenty of exceptions out there and so on.... but I think the majority of women do not have good sexual experiences with people they've only been dating a few weeks. If a guy has only been dating you a few weeks and it's casual, it's VERY likely that he will have the attitude that he will try to "get away with" as much as he can, push his sexual desires on you to the max, and see your preferences as an obstacle to get around. There's a reason why many of these guys want to keep things "casual." If it's "casual" then in their minds, they get a free pass from caring about you or your feelings.
Why don't you find a nice boyfriend, and develop a committed relationship for a few months, and get to the point where he's repeatedly DEMONSTRATED he cares about you and your feelings and is willing and able to put your needs above his preferences when appropriate, before sex is even an option?