One of my big toes is swollen and a little red, sore to walk on, and to touch. Mainly sore on the mid-toe joint. What could it be?

Infected Big Toe. Barring trauma, your big toe has all the signs of infection and you probably need antibiotics ASAP. Go see a physician because left untreated an infection can spread and lead to very undesirable consequences. Best of luck to you.
Need to examine. It is not feasible to provide a meaningful opinion without taking additional history, physical examination and may be some tests. It would be prudent to see your doctor. However, gout needs to be excluded in a male with big toe swelling and pain.
Wish you good health! - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form.
Practice safe sex, if you have sex.