Dog limping after walk

Breed: Welsh sheepdog

Age: 8

Weight: 35kg (slightly overweight)

Castrated: yes at 4 y/o

Conditions: Chronic pancreatitis, hip and back issues, overall stiffness in hind quarters, anxiety, dog reactivity, many allergies

Medication: 64mg reconcile daily, 900mg gabapentin daily, 1500mg paracetamol daily

Exercise: 1 walk a day lasting 20-40 mins (depending on overall condition on day), 10-20 mins of mental stimulation games

Location: north west England

2 nights ago my dog was limping slightly on his evening walk, later on he yelped loudly while getting into bed. Now he has a pronounced limp on his front right leg, is stretching a lot, and showing stress signals such as lip licking and yawning. He’s not lost his appetite at all and is still showing interest in sniffing and cuddles. Limping has stayed to the same leg. No event happened on the walk which I could see attributing to this level of pain. Both myself and partner have throughly looked at his paw, nothing has been found. He is not holding the paw up in the air.

He’s was bitten by a tick 1 week ago, which was removed while still very small. Area is a little raised and has a small scab but not red or showing a rash of any kind.

Any advice is welcome, he is a senior dog with a history of pronounced pain in is back and hind legs but he has never had any other pain last over a day.