What Causes Lightheadedness Inspite Of Normal Blood Tests?

Question: Hello!
I had a 5 month battle with C Diff at the beginning of last year. During that time I had problems with getting lightheaded after eating amongst a host of other issues. The C Diff and the lightheadedness resolved last May, but over the last two months I have had a return of some gastro symptoms, some acid reflux, and a big problem with lightheadedness especially after eating and drinking. Soon after I eat I get lightheaded and I feel a dampness in my nose and sinuses along with some pressure. The air I breath out from my nose is moist and I can feel the moisture on my upper lip. This usually resolves after an hour or so.
I have been tested for CDiff along with other possibilities through stool samples...all negative. I have had extensive blood work for the usual things and everything is fine. They also did an EKG and CAT Scan of my brain...again all fine. At this point both my gastroenterologist and my internist are done with this. My gastro told me to set an appt for follow up in 4 months and my internist told me that " she doesn't know what I expect her to do about this". Both are at a top university hospital in a large city! I am at a loss as I still have these symptoms!!! They each suggested stress and anxiety, but that really doesn't factor in as, aside from this issue, I am in about as peaceful a place as I've been in years! I have continued to try to figure this out using the internet and have come across many people who are left in the cold by doctors, unfortunately. I am desperate for some help as it is very difficult to carry on daily in my professional life as a teacher and my personal life with the constant threat of lightheadedness!!!!