Hello dear user! I have gone through your query and understood your concerns! Thank you for sharing them on healthcaremagic. Well, there are cases where patients have been complained to have knee swelling or pain, while taking medications. These are rare cases and mostly happen when used Bactrim to treat infections. It looks like it is a side effect of the medication since you hasn t had any traumas lately to explain knee swelling. The swelling will go after some days you quit the medication. Just keep it with cold compresses to remove the swelling. You may need antiinflammatory drugs such as ibuprofen to ease the swelling remove. Take joint supplement to ease the recovery. If it does persist for too long and gives you disturbs, please contact a doctor for further examinations. I hope this answer was helpful to you! Please kindly rate it as helpful and write a short review about your experience with me! I would appreciate that a lot. Thank you and best regards! DR ERIOL.