My rescue domestic short hair male has had a recurring swollen lip for the past year. He has been getting Convena injection every six weeks, now he is swollen after 9 days. I have switched to Hypoallergenic Hydrolyzed food, yesterdays news litter, stainless steel feeding dishes, and all plastic eliminated. He is only 2 years old, they want to do a biopsy. Has anyone been through this. What could it be??