Wearing dressy clothes in the "lab"
It is perfectly appropriate since most university dress codes for students is to make sure nothing offensive or too revealing is worn (local definitions for both of those are widely variable). It sounds like you are having trouble working out if it is simply that you are unusual or if it is actually a problem. The simple solution is to ask some of the folks in your lab what they think. 

If it turns out you are worrying on their behalf when they don't care, then keep wearing nice clothes.

If it turns out they care then you actually need to address that, whether by asserting your right to wear what you choose to within the official dress code or by making adjustments. Since clothes are social markers it might be what they perceive to be your statement that is the problem and not the clothes themselves. 

It is always possible they are glaring at you for completely unrelated reasons. Again feeling that out is worth your time. 

A personal story, I wear Hawaiian print shirts every day while teaching. One day I wore a plain button down shirt and my students asked what was wrong. It was laundry day. So don't discount the possibility that the only thing going on is that you stand out from the norm and nothing beyond that.