I have a cortisol level of 0.8. can that cause weight gain, extreme fatigue, joint pain. low bp, heart palpitations? what should i do?

Complicated: Normal 8 am cortisol is 8-23 micrograms per deciliter. Since you don't use units, it's not clear if you're normal or not. Moreover, even if it's low as I think you're hinting, your Symbicort (budesonide and formoterol) may have suppressed it. A cortrosyn stimulation test is needed. Finally, low cortisol could cause fatigue and low BP, but not the other symptoms. Clearly, you need to stay under your doctor's care!