Hi Arsalan,
My name is Igor, I have 12 Microsoft MVP awards. It's a pleasure for me to help others and I'll do all my best to help you. I'm sorry you have a problems.
Seems this is normal for you hard drive. It uses SMR technology, it is used in many new hard drives. It allows to increase drive's capacity up to 15-20% but may cause slowness in some scenarios.
Your drive writes a data not file by file but a mash of data as they are coming in to device. Then device reorganize the data in correct order. This reorganization is very slow process, appr. one write per second, so drive is heavy loaded for a long time even without noticeable read/write operations.
You may verify SMR presence. Run command prompt as administrator and run a command
fsutil fsinfo sectorinfo c:
If TRIM is supported, you have SMR drive.
Such drives are good for data storage but bad for a system. Sorry for bad news.