NEED HELP ASAP!! My car has been leaking fluids out of somewhere! It Will Not keep water/coolant in radiator! Heater will not blow out warm air! Keeps overheating! HELP!!?

Ok, so my car is pretty old I know.. Worst
part is its all told in the mileage I have on it,
as it reads; 373,019 as of right now!! I've had
this car for almost 1 1/2-2 years now, it had
250,000ml on it when I got it. I've NEVER
had ANY problems with it other than
needing to change the tires, do alignment,
bearings and all that good stuff. About a
week ago, I noticed my heater wasn't
blowing out warm air when I was stopped,
like at a stop light, parking lot, or just
running in the driveway. Then I seen a green
like liquid started leaking out into a pretty
big puddle under my car, and its never
leaked before. Then after I got in it n drove
away the heater was no longer blowing out
any warm air at all! Not even while driving! It
was freezing cold!! So after driving for about
20-30mins my check engine light, my oil
light, and my temp gadge all came on at
once I obviously knew something was
seriously wrong so as I was going 2 pull
over my engine seized up on me I had no
power, no control at all! I could barely stear
the car off the road! It was smoking really
bad at this point! I had to wait a long time
before opening the radiator cap and then
putting in coolant since it was all of a
sudden bone dry. Since then I've tried to
only drive it when I have to, witch has been
hard since I'm a single mother that doesn't
know a whole lot about cars and its my
ONLY transportation to get my toddler and I
around. At first it after filling it back up with
water the heater would get hot again and I
could only drive if I had the heater on cause
as soon as I turned it off my temp would go
up. After having it overheat 2 or 3 times, the
engine seizing up on me twice it blew my
temp gadge! N now my heater won't get
warm at all! N I can't tell when it's getting
hot to pull over to put more water in so
when it does overheat I can't stop n fix it
before its too late, so my engine seize's up
every time! I've been told it could be a few
things, my heater core thermostat? Or my
water pump? But its obviously leaking from
somewhere underneath the engine near the
passenger side of the car kinda twords the
frount near my tire. So could it be a hose
that's busted or what?! I need help SO BAD!!
And I can't afford to take it to the shop, nor
can I afford to completely f*$% my car up to
where its just a goner! I can no crack my
head gasket or blow my radiator! So I need
to fix this today! I ordered a water pump and
its ready for me to pick up I just don't wana
pay that $ if that's not the problem, I do
know that I now have to replace my temp
gadge no matter what so that is a "positive I
need to fix". So any helpful ideas?! PLEASE!!