Will eating fatty/calcium rich foods like tahini butter give false positive blood work 12 hours later if you have low calcium? Fat feeling in stomach.

No. These won't mask a true blood calcium problem. I'd urge you to get with a dietician since you acknowledge a need here, and your physician or health educator to learn exactly what's going on with your calcium homeostasis. You're an adult now with what sounds like a significant health problem, managing which will require you to be proactive.