Many nonprescription supplements can cause lightheadness!
If your doctor said you have a sinus infection that could be the problem.
You don't need to be congested to have a sinus infection.
Your doctor diagnosed your condition as a sinus infection and you are taking meds for that, so hopefully that will clear up soon. Your comment that you are taking "a lot of supplements and caffeine" leads to other issues. Caffeine can be overdone and may bring problems. In moderation, coffee is good for one, but too much caffeine from whatever source is dangerous above certain levels, especially the more recent powdered caffeine. Supplements often sound good, but they are unregulated, so one never really knows what is in them nor if the ingredients are beneficial.