Inasmuch as sweat pants are comfortable, they are really not all that acceptable as college attire.
There are many brands and styles of clothing. Having worn sweat pants all along and then changing into jeans is understandable a big difference in fit and feeling and something you may just have to get used to. You can begin with very loose fitting jeans. My son was a wrestler and had a wrestler's body with large calves and huge thighs full of muscles. He found that Wrangler Jeans and Husky cuts in other jean brands fit him well. You should find a jean that you are comfortable in. There is surely one out there, you just have to find it.
Also, cargo pants are comfortable and some of them have an elastic waist back or elastic in the waist line sides for ease of comfort. Also cargo pants are not form fitting either.
My son also, since he was a toddler, hated tight clothing, tags in his clothes and other clothing features that his body just could not take. So, I shopped for upscale designs in sweat pants without elastic in the leg bottoms. The trick to looking good is jersey type clothing is to wash them often so they retain their shape. There is nothing worse than the appearance of bagged out knees and rear end sag in clothing.