Should I refrain from drinking lemon juice while managing my diet?

I am on the Danshe diet. I am currently on day 5 of week 1.

I'm curious, I really want to have coffee at lunch today, so I'm trying to hold back.

I made myself some lemon water.

I filled a large tumbler with water and squeezed in an entire packet of 100% lemon juice.

I drank about half of the water and then refilled it once more.

I really diluted it, but the problem is I got diarrhea right after drinking the lemon juice.

Could it be because my intestines have weakened due to the Switch On Diet? Should I avoid drinking lemon juice, even if it is diluted?