Eight-month-old baby, has been refusing food for three days, being fus…

Eight-month-old baby, has been refusing food for three days, being fussy, sleeping poorly, yesterday's temperature rose to 38.1, gave him ibuprofen, it didn't rise anymore. No symptoms of colds at all. I think they are teething, lower teeth have grown, but absolutely did not bother them. The gums are swollen and upper. Has anyone experienced this? What helped? How long did it last? Thanks in advance for informative answers!