2001 Dodge Neon

I have a very basic understanding of the
combustion engine, bit I cannot figure out what is
wrong with my car. While idling at a stop light  the
engine was sputtering a bit, no backfire or
anything, but when I gave it gas it bogged down
and it would move in any gear. I checked the air
filter, that's fine. I guessed that maybe moisture got
into the fuel line and froze since the high temp for
the last week was 12 degrees. I added a bottle of
Heet, but it isn't even turning over anymore. I
haven't replaced plugs or wires in a little over a
year, but it had gone years without needing new
plugs or wires so just over a year seems too short.
I've never replaced the coil. I have been getting
terrible gas mileage for 2-3 years, progressively
worsening, and I ran out of gas on the 5th, but I
have filled it twice since then and not let it get
below 1/4 of a tank. Any suggestions would be
appreciated because as a single mother/student...
I cannot afford a new car or a mechanic.