Red spot on soft palate. I'm not sure if it's due to a gum disease or due to oral sex or drinking?

Red spot on palate. The red spot could be caused by any of the things you suggested. Best thing to do would be to visit your dentist if the spot does not disappear within 5-7 days and have the dentist check it out.
Yes, yes, and yes. All three are possible, but they are not the only possible causes. Please see you Dentist for an evaluation.