Whats wrong with the speed?

I have Cox Internet Preferred 150M plan but have some problems with internet speed last few days. My zip code is 90274. I did everything I need to solve the problem but nothing happened. Today the speed was worst so I can’t work with my steaming project and took the pencil in my hand. I’ve found the following download speed:

15:05PM………….20M

15:24PM………….3M

15:26PM………….121M

15:27PM………….141M

15:28PM………….144M

15:29PM………….36M

15:30PM………….6M

15:31PM………….8M

15:32PM………….24M

15:33PM………….18M

15:34PM………….24M

15:35PM………….13M

15:36PM………….2M

15:37PM………….1M

15:38PM………….3M

15:39PM………….24M

15:40PM………….23M

15:41PM………….22M

15:42PM………….10M

15:43PM………….10M

What’s wrong with my internet? The speed range was from 1M to 144M? What I need to do? Thanks in advance!