Everything is going wrong with my car!?

Upon first receiving my 2000 Plymouth Breeze it worked great. After about a year of
owning my heat stopped working, but with it nearing spring, I reserved that for a later
issue. Soon after, my car started overheating. I bought a bottle of leak guard, refilled it
with coolant, and it was fine, for a month or so. Soon, I was leaking coolant faster than I
could buy it, getting to the point where I was refilling it every day before I got it fixed this
past August.
I had my water pump, timing belt, and radiator replaced for nearly $1000, with a 90 day
warranty. As it started getting colder, I enlisted the help of a family friend to help with
the heat issue. (Also, by this time my air only worked if on the highest setting.) The
friend tried to flush some gunk out, and found air pockets surfacing when he flushed my
coolant. He assumed I needed a new heater core, which would take longer to fix than I
had time for, and we settled with flushing some gunk out of some tube that got some
sort of heat flowing through. Never enough to make you take your coat off, but as long
as I let it heat up before I started driving, it was a comfortable heat which was fine for
me. This took place mid-November.
Fast forward to last week, when I noticed an insane amount of coolant leak from my
car. My car has been overheating once again. I, again, bought leak guard and coolant,
this time to no avail. I can't drive more than a few minutes without my car overheating,
and any heat I've had for the past month has quickly vanished. I have no clue what to
do here. I don't know if my August fixes were faulty or if my car just has no hope. It
doesn't help that I am car-clueless. Please help me out! Any ideas on what could be
going on!?