Why is my IPAD II Low Storage?

I was checking the available room on my IPAD as I had added quite a few apps recently a few of which took a great deal of room. When checking for space left I was shocked to see I had only 585 MG remaining to use. I immediately proceeded to remove many apps that were not needed and the very large apps. I rechecked and my space used and space remaining was much better as it was showing 10 GB Used (approx) but there was now 1.8 GB Available.

However the next morning I was rechecking just to make sure all was ok and MY AVAILABLE HAD DROPPED TO 735 MG ! I did not add or make any changes during the time I thought I had fixed the problem and this drastic drop; for what reason I haven't a clue? Now today it has dropped again and this time it is down to 185 Mg. Again I had made no changes to cause this drop to happen. I have had this IPAD for 3 years and have never had anything like this happen.

Can anybody help me? Soon I will have 0 left to use & I will just disappear! Joking aside, I have checked the manual and searched the web with no success. Please help!