What is wrong with my Dog?

Hi, my do, max, is 5 years old and a er spaniel, poodle cross (apoo) he has numerous amounts of health problems including epilepsy and a low theiroid. he also ways 30 pounds and is abnormaly large for a apoo. we believe all these problems are due to poor breeding. but latly, my dog has been lathargic, but eating fine... the other problem is that he cant jump on the couch anymore to snuggle, he starts stuggling to get up and crys! he is very tender on his lower half and cant seem to put weight on his back legs. my dog is usually very happy, and off-the-walls crazy! this isn't normal for him, he doesnt even want to play ball! i'm thinking it might be Hip-dysplasia because i know thats commen with ers, but could it be something more serious? and if it is hip-dysplasia what can they do to help him? thanks for your answers...