BG's Pretty Steady - Other Issues Emerging...

Buddy has gained all the weight back that he lost during early stages of his diabetic journey. Now he is overweight - only eating wet foods (mostly Fancy Feast and Nulo and Tiki) and is being fed 4x day (total less than 6 oz). He has also become inactive - was not sure why - but this morning, he vomited his morning meal (about 10 minutes after his Lantus dose, of course), and his Left back leg became non-weight-bearing. I was freaking out and called the Emergency Vet who just said if his leg wasn't cold, it likely wasn't a clot/embolism... He has luxating patella issues (tore cruciate ligament in right leg 2 years ago and had basically, knee reconstructive surgery). Husband took him to Vet today - Vet thought it was great that Buddy's only on .5U Lantus; said he needs to lose some weight by small decreases in food amount per feeding, administered fluids d/t vomiting episode, and he put his knee back into the socket. And that was that. Buddy is still limping tonight - and staying on the floor (not into jumping). Not sure if the increased inactivity is because of the patella issue or something else.
Any suggestions from anyone who has had/has a diabetic cat with IBD, knee problems, etc would be greatly appreciated. Or, even if you haven't had a multi-faceted cat like Buddy - suggestions appreciated
Always something....