100% disk problem windows 8.1?

So I got this lenovo G510 not two weeks ago, and everything was going great until yesterday when my laptop started running slow. Games are slow and not smooth and sometimes apps don't respond and touchpad freezes for a while. I checked task manager and the disk appears to be full (100%) even though I'm not running a lot of applications. Under processes, it shows one app that is using a lot of disk, for example 67% and the others are normal. When I close it another app uses that amount and disk is still 100%. I ran anti-malware scan using the latest windows defender and also the latest malwarebytes, and no threats were detected ( no viruses as well ), so I went online and tried several solutions but it still doesn't work. Note that it doesn't happen all the time.
oh, and here are my specifications:
- Core i7-4700MQ.
- 8GB Ram.
- 1TB HDD.
- Windows 8.1 x64.