Hi.. Thanks for the query.. No, it does not look like the swelling under the jaw and sore gums can be due to the diclofenac gel, rather it looks like there is infection in your gums or tooth/teeth that is causing the following symptoms.. I would suggest you to consult an Oral Physician and get evaluated and a thorough clinical evaluation and investigation like x ray if tooth decay is the cause will be ruled out so that treatment can be initiated accordingly.. As of now consult an Emergency room or a local physician and get evaluated and a thorough clinical evaluation will be done.. You can be advised antibiotics like Amoxicillin and anti inflammatory painkiller like Advil can be advised to you for relief.. Along with it you can do warm saline gargles and do alternate warm and cool compresses over the swollen glands.. Hope this helps. Regards..