Painfull gums at back no teeth there dentist say they look healthy had extraction week ago opposit side had a bit of infectioncould it be that?

See your dentist. Your condition is a gum abscess not tooth related or due to impacted tooth. If not treated it can worsen and result in the destruction of bone tissue. If treated the prognosis is excellent. See your dentist for examination, x-rays and treatment. .
Opposite Side. Do you mean left and right, or top and bottom? Pain can be referred from lets say, the top left to the bottom left, but not the bottom left to the bottom right. Are you wearing a removable prosthesis? More info needed for a definitive answer.