Im new here, My ethernet is slow, recieves and sends slow Kbps, pls help me

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im new here, im connected with ethernet, the internet speed always test shows 130-150 Mbps but my internet sometimes is normal but most of the time is slow, sometimes doesnt recieve or send Kbps and if they are circulating its always like 16Kbps or really low numbers, I saw on a site that I should install wireshark to see the problem, but what am i supposed to do? pls help, i used tu have good ethernet speed, now its just slow