There is 2 reasons for this the first 1 being the water inlet valve needs adjusting or in many cases this needs to be replaced.
The 2nd one is due to the cistern washer has worn and needs replacing.
There are various reasons drain get blocked
Kitchen drains get blocked to grease entering the drain or food scraps Main drains can be blocked by tree roots
The hot water system you have may not have enough capacity if this is a storage unit The heater may need to be serviced to keep this running at peak performance
In most instances if this happens you should check garden reticulation is not leaking. Check toilets are not constantly running
You can check the reading on your water meter then check the next morning
If you have any doubts call a licensed plumber to a water pressure test