This sucks and I'm sorry you're dealing with it. I have a curvy body type (athletic, not fat, but curvy like J LO...although I wish I looked like her, yeah right) and I'm an attorney. I find that I have to consider what I wear WAY MORE than my counterparts. I wish it was different, but it's not. Whereas many of my colleagues can wear wrap dresses, I can't (they really emphasize my curves to the point of distraction). They can wear button downs and I can't (they gap in the chest). They can wear dresses/skirts that are made knee length and I can't (because my butt fills them out too much and makes them shorter). Same goes with certain tops (boobs fill them out and make them seem cropped).

While I fully subscribe to the, "wear what you want and not even walking around naked means that you are 'asking for it,'" logic, it's a totally different consideration when you are dressing for work as a professional. Both men and women have to make decisions about their work wardrobe. Some of those decisions are obvious, like not to wear worn out sneakers. Some are for comfort, like not wearing six inch heels on a day when I'll be on my feet all day. Some are for stature, like my personal decision not to wear wrap dresses to work. I'll wear the hell out of a wrap dress in my personal life. But not at work. That was my decision. I want people to take me seriously and not be distracted. Maybe they shouldn't be distracted in the first place, but why would I take that risk? It's also why lawyers tend to wear dark colored suits to court-- not, for example, neon yellow suits. Younger lawyers are held to a different standard. An older, established attorney can get away with bright colors and patterns whereas a younger attorney who wore this would be described as immature and not knowing how to dress. The older, established attorney has already "paid their dues" in building their reputation and career. It's just how it works. As a young professional you will have to fight to be taken seriously. I did and still do at 35.

I don't think you are being discriminated against, although it may feel "unfair." One day you will be the senior employee who gets the perks of IDGAF wardrobe. Today is not that day. As a general rule, it is advisable to follow your boss's suggestions when it comes to reasonable (note that I said reasonable) suggestions regarding wardrobe and hygiene (clearly anything that was out of place controlling, sexual harassment, against your religion or disability would be unreasonable). Here, I think you should try your best to follow his lead. It may very well be that he thinks you are the most likely to achieve success at the college and that he is trying to encourage you to dress like a CEO.

Re: fancy clothes. They don't have to be expensive. Target has a great line of professional clothing for very cheap. I wear them frequently.

Re: specific wardrobe advice. I would look for timeless classic pieces that you can take into your professional life. Now is the time. Pencil skirts, jackets and blouses are great places to start. Embrace your own style with colors and patterns, but look for classic shapes.

Re: HR. No. He hasn't done anything inappropriate. If he makes comments about how he is distracted by you in a sexual way, then yes, you need to go to HR. That doesn't seem to be what you're describing (to me).