T.O.
HI, both of my boys did that! My 6 year old does the same thing now. Some of it is control, some of it is truly he does not like the way certain clothes feel. At least for mine it truly is that they cannot stand the "rocks in the socks" (that is what they called it) feeling of the stich line (the ends that have the stringover the toe.. I can't explain it, I agree it really feels like a small rock in the socks..but it is a valid complaint!. I have to buy no line socks without that stich line (easy to find- gap, old navy, tony hawk, some addidas)
They are also sensitive to certain shirts, underware, and even some pants. Mosly it is the tags, and sewn on logos etc...It is not fun, but I make them try on clothes before I purchase and make them let me know how it feels. It somewhat kills 2 birds with 1 stone. They can conrol what they own to wear, (i obviously only show them clothes I would buy and they pick from that) It sounds like I am spoiling them... but my 6 year olds preschool teachers son did have a valid sensory disorder, and clothes was a big part of that. My son had the same exact problems her son did. He also had more severe issues with other sensory things, but the clothing truly can be a problem as well. The extended temper tantrum... that is a control thing. (we still have those once and a while).
Hang in there. Good luck. hopefully this helped you some... It is not fun and can be VERY frustrating. our pediatrician helped us with that too:)