Hello, Welcome and I hope to assit you. Having the need for a root canal indicates that you had an infection. Your body needs time to heal and can suffer from the effects of an infection spreading. Did you take a prescription antibiotic since you had a prescription for pain medication? The antibiotic is effective in controlling the spread of the infection and not just a few hours of relief. To be effective you must complete your antibiotic prescription. Pain medication only treats your uncomfortable situation for a specific time. You should not need the pain medication for a very long time if you have completed the root canal. Please check with your dentist concerning an antibiotic and update your concerns with your dentist. Make sure you have all your teeth checked and keep up with good routine dental care as well. I would not consider your reaction a side effect of your pain medication. Medications can irritate the stomach and throat. Dry mouth is more common than exra saliva. You describe symptoms of a sinus infection. You may have post nasal drip which can irritate your throat. Tonsils are one of your first lines of defense to fight infections. A sore throat accompanied by inflammation can cause difficulty when you swallow. So you may have a respiratory infection. This may require a trip to your physician to treat seperately from the root canal. Rinsing may offer some relief. Please discuus these concerns with your dentist. Your dentist will assist you in determining if you need to see an additional doctor. Thank you for your inquiry. I am glad to be of further assistance should you have additional questions or information to share with me.