Why am I constantly tired and bloated?

[AngelCollins323]

For the past 2 years I've had stomach problems. Bloating, nausea and stomach cramps daily. The nausea isn't as severe everyday but it's pretty bad. Earlier this year I had a gastroscopy that revealed that I had nodular gastritis & a yeast infection in my oesophagus but even after the medication, my symptoms are still the same.
Since about March 2017 I've felt extreme tiredness everyday. Usually sets in about 2 hours after I wake up. Then I've also had headaches for years but since mid 2017 I get these weird headaches about once a week. It feels like my head it overheating even though it's not warm to the touch & it gets worse as the day goes on.
I've seen several doctors. They tested for multiple things but my thyroid is fine, I'm not diabetic, no food allergies & my iron is okay. They refuse to test for anything else & they're insisting that it's a depressive episode but I know what that feels like & it's not this. They say the stomach issues are separate. I don't know what else to do because I've been on supplements for a long time & there's been no change.