Lately (~2 months) been very thirsty after sugar consumption, and tired/sleepy after carbs. fbs within normal range 8 months ago. no other symptoms. ?

Rule out diabetes: The symptoms are suspicious for blood sugar problems. You could have a fasting blood sugar that falls within the "lab normal" range and still have a problem. There are other tests you should have done to rule that out (like a hemoglobin A1c or glucose tolerance test). It is important to keep in mind that something else could be going on so see a good primary care doc who can look at the whole pic.