i have a 12 week old hamster. i bought him from a pet store when he was 8 weeks old. he is very lively and friendly, but has something large at his rear end near his tail. its getting bigger, it has no fur on it. just like a pink sack.he doesnt seem to be in pain, eating and drinking well. even exercising at night. is there any possibility he is a she and pregnant, or does he need to see a vet.