Had oral sex. White, sore spots came up and went away after few days. But came back, and now I have sore red throat with yellow-ish spots? Oral thrush?

Exudates? . Exudates can be common to a sore throat either be infectious or not. Oral thrush while not as common are white and have a plaque like appearance usually found in either immuno compromised states or usage of steroids. .
Get checked. It could be thrush, which is a fungal infection, but you can get other infections, such as chlamydia and gonorrhea, in the throat. You need to get checked.