Cumulative count in grafana

I need to get a graph of cumulative count vs time.

I have 5 App servers , each of them will send individual count,timestamp to es.

I need to add them and put a graph which shows cumulative requests.

Data from App1 : { count:1, timestamp:$epochTimestamp}
Data from App2 : { count:4, timestamp:$epochTimestamp1} …

So my graph should show 5 , however the “epochTimestamp” and “epochTimestamp1” are different values and they keep varying there is no set interval between them.
For this data when i do sum(count) , sometimes it shows 5, sometimes it shows 1, sometimes 4 depending on time interval. How do i get a graph where it does sum and say 5 and whenever the next value comes it just adds.

How much data is the Prometheus is generating on disk per specific amount of time such as hour, 6 hours, 12 hours, etc.?