Huge pagefile allocation maybe?
Turn it down to 1.5x your physical memory, so for an 8GB system you would have a 16GB page file - this is best practise.
My opinion/not best practise: - I turn mine off completely, forces my PC to use the much faster physical RAM to it's fullest, and it never fills 8GB.
EDIT: Just toclarify, if you have 8GB page file, there will be an 8GB file on your drive called pagefile.sys
The more virtual memory you have allocated, the more drive space it will use. If you are currently letting windows automatically manage the size, it could potentially be causing the problem you're having
the other possibilities are malware (get malwarebytes anti-malware and run a full scan) or perhaps Hibernation settings being weird (huge hiberfile.sys file)