Does your blood work show you are lacking in any vitamins, etc. What’s your kidney & liver function like? Your sugar levels?
A post nasal drip will often make you feel nauseous.
I suffer from postural low blood pressure so suffer regularly from head spins & loss of vision. My energy levels aren’t great either & have had a few hypoglycaemic episodes - cold sweats, drop in blood pressure, drop in energy, vision narrowing, nose running, etc. I had these before I lost weight but just experience them more often now.
But I’m no expert. I encourage you to get some detailed work ups from your medical team sooner than later.
Good luck.