Hello Inkscape. My name is Finn Downey. And I have been using Inkscape to make a drawing to put on Deviantart but I am having a slight problem. 
It seems that the bigger my drawing gets, the slower the website seems to act. I have especially noticed that whenever I try to change the width and height of the drawing in the document properties, the numbers seem to automatically revert to what they were before I changed them. And whenever I select something to try and move it, it moves so slowly.

do you know what is wrong and if there is anything that can be done to fix these problems?

please send a reply. Thank you kindly.