Do I have an infection, if my throat hurts a lot today?

Maybe. Bacterial, fungal & viral infections can cause your throat to hurt but so can breathing dry air thru your mouth (rather than moisturized air thru your nose). The drying effect can make your throat sore. Some folks are bothered to the point of complaining of pain from post-nasal drip. If you have really bad heartburn, that can irritate your throat, too. Go see your family doc for an initial eval.