3 year old has 99.3 temp, won't eat, laying down all the time, no energy. Any ideas? Also been coughing and sneezing for the last week.

Needs Doc visit. First, 99.3 is not a fever. Second, coughing and sneezing for one week in a 3 year is usually a virus that will resolve with no intervention. What concerns me is the lack of play, energy, and eating. I would recommend a doctor's evaluation for the lack of eating and decreased activity. .
URI symptoms. With coughing and sneezing and low fever, it sounds like your child has an upper respiratory infection. This is usually viral and can often last 7-10 days. If he has any breathing difficulty, refuses to take fluids, spikes a fever over 101, or is not interactive when awake, he should be evaluated by your doctor or urgent care. Otherwise, give it a few days and encourage fluids.