Low water pressure "help"

I have just moved into my house which is about 5 years old and I seem to be having an issue with my water pressure.

Every time I flush a toilet I can't use the cold water tap (nothing comes out) until the toilet system is full and then it works fine ? Is this normal as I have never experianced this before.

Also the water pressue in the whole house is very low with no real pressure any ideas on how I can improve this?

Many thanks
Kind regards

If the stop tap to the house is wide open (check that) then it may be that the washer has become dislodged hence blocking/ restricting flow of water.

Thanks, I will check that first thing.