In need of serious help with parents

Hello guys, i'm now on 15th day of fasting (doing good), problem is few days ago i've made the HUGE mistake of meeting my family, causing them (anxious and paranoid people) to get really worried about my weight, which decreased during the fast.
I told them i've had some intestinal virus which caused a quick weight loss, but now they are requiring me to do a medical examination.
I already agreed to test for common parasites, but now realized that stool examination is not easy while fasting, and now i don't know how to satisfy their paranoia.

I really need to get out of this situation in which they are watching over me but i'm having a difficult time finding an effective solution.
I'm 22 but they still treat me as a kid and they warned they will send doctors where i live if they won't be reassured. All this is a huge source of stress in a delicate time like this one.

Telling them i'm fasting could lead them to think i'm harming myself and things could get "psychiatric" so i don't think this is a good solution.

Please i need some advice.

Should i interrupt the fasting and tell them?
Should i find a conventional doctor to check me up and ask him not to write about the weight?

Bad situation.

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