Slow internet speed problem

I’ve been having quite a lot of problems downloading through the launcher recently…
I saw that I had only a very twitchy 300kB/s on the launcher, going full rollercoaster down to 0kB/s and up again, so I decided to try downloading on steam to check if my internet was the problem : 5.4MB/s.
I don’t know why the launcher started doing that but it really ■■■■■■ me off…
Anybody knows why this happens ? Thanks in advance !

omg pls i need that answer, i have the same problem downloading fortnite