My One Year Old Dwarf Hamster Is Losing Large Patches Of Hair And Has Started Sqeaking Loudly In Pain While Lying In His Bed (only About Once A Day). What Could Be Wrong?

I have had numerous hamsters and this has been the first to lose large patches of hair and squeak in pain without provocation. He is almost a year old, a dwarf, and very well taken care of. He gets a variety of foods and vitamin supplements. He tends to like baths with water, which may not be good for a dwarf, however. Lately he has stopped keeping himself as clean as he used to. I just moved, so he could be stressed, but I am not sure and I am quite worried about him. Thank you!