Hello Ma'am
Many thanks for your query. It seems most likely that your baby is now getting his normal set of primary ( milk teeth) considering he is 7 months old. This should explain the pain and swelling which is expected to accompany teething.
Next Steps
While it doesn't seem anything to worry about, you can always have a pedodontist or child specialist dentist have a look and confirm that it's indeed teething. Some painkillers may help but they are best prescribed by a dentist who has the opportunity to examine your baby.
Health Tips
Please make sure that the area is kept clean, especially after feeding.