My Gums Are Red And Swollen, Only On The Bottom

My gums are red and swollen, only on the bottom teeth. It gets worse when I eat. There was bleeding at one spot but not anywhere else. They are very painful. It is difficult to eat. I went to the dentist and she gave me some mouthwash. I also take penicillin for Lyme disease. Can this be an allergic reaction to penicillin. I've been taking it for 9 months and the swollen, painful gums showed up a week ago.