Yes a luxating patella is the first thought to cross my mind or even a
rupture of the cruciate ligament. Your veterinarian needs to check these two out very thoroughly.
Being a small dog, a modified Robert Jones bandage might solve the problem if applied fast and it stays on for 3 weeks.
If after this it does not solve the problem a surgery will have to be
attempted. Best to get back to the vet asap.
Learn more about Pomeranians and their health problems