Over heating weird problems

A year ago I changed my thermostat and molded
heater hose when my car was going over the
hotline period go forth almost a year. Going over
the middle line it is leaking when it was 20 degrees
outside after driving for two minutes Other than
that I haven't seen much leaking when it did it was
underneath the passenger side.put a new
thermostat in. After heater is on high and I'm on
the freeway I'm fine. have to keep pouring coolant
and it or antifreeze Rather. no white smoke coming
from the tailpipe don't hear any noises like the
water pump the coolant is boiling hot Now the heat
is going in and out while it's going sometimes 3/4
of the way to the middle line or sometimes over
the line when I do have to turn the heat on to get it
to go down I'm not  hearing anything water pump
radiator heater core how would I check any of
these unfortunately and by myself and don't think
its the head. However I can and have done alot of
work myself wheel bearings etc. I don't have
thousands of dollars to take to a shop, but have
someone that can replace what it may be or I can
myself please any help is more then appreciated!!!!