CPU speeds drop when Minecraft Bedrock Edition is open

So this has been happening for about a month. Whenever I open Minecraft Bedrock my CPU speed drops to about 0.7-0.9 GHz. This makes playing almost impossible as the lag is unbearable. I can't seem to find a connection between this issue and a recent computer software or Minecraft update. I am not sure whether this is an issue with the game or an issue with my computer. When I contacted my computer manufacturers, all they said is that this is an issue with the program. Any help would be appreciated.