Custom Event Report Chart: Group By and sum events in a period

Context:

I have a custom event that is fired every time a user sees and specific screen, where the user can see another user's response to a question

The information that Im sending is UserId, QuestionID

What Im looking for is the number of responses to a question by day or week. The problem is that an user can see the response multiple times.

So I need to distinct by user Id and group by question 

Working with the Data Explorer I've been able to create this filter

MyCustom Event measured by total
group by Question Id

Thats end up in a Chart where I can see the number of events fired by QuestionID.

What I really need to know is the total number of questions that are reviewed every day.

How can I achieve this, with the event that I'm sending? Im looking for the total number of questions  reviewed by week for example

Im looking or something more like this where the gray box is the sum of all the questions IDs