Flat battery, EPC Warning, Central Locking and Steering fault

I need some help!

I started my car this evening, drove 4.5 miles and when I put the car into reverse to park, the power steering failed and the warning light came on.

I turned the engine off and tried to restart as I thought it might be a simple fix to "re-set" the steering, however, the car did NOTHING!!! The engine did not turn over, although the lights on the instruments were on. I had to physically push the car out of the middle of the road to park it.

This has happened once before on a 120 mile trip (minus the power steering fault) After this happened to me, I jump started the car to get it home, and had the battery changed. (About 3-4 months ago)

The car has been ok since then, but the battery doesn't seem to hold a charge. I'm not certain that there is no problem with the alternator, however, there have been no battery warning lights on the dash. Sometimes it's sluggish to start, and other times, it starts without issue at all.

In addition to this; the central locking on the rear passenger's door has only worked intermittently for the last couple of days. (Window still works fine, so there IS power going to it) Just can't hear the lock working when the other doors lock/unlock.

After charging the battery for a short time at my dad's house, the car started and I drove it home however, after starting the car after it's deadness the EPC warning light has come on and has stayed on for the 4.5mile journey home.
When I got home, I parked and re-started the engine to see if this would re-set, but after a sluggish (battery still limp) start, the EPC light is still on. I drove at around 55mph on the way hojme so it hasn't gone into "limp mode"

Can anyone help? Even if it's just one of the issues.
I do have a light that appears to remain on in the drivers electric window control unit (child lock light) would that be enough to drain my battery or could it be the central locking that's draining it?

Help help help!!!

(I'm in Portishead, North Somerset - if anyone in the area has VAG-COM to help diagnose issues that would be fab)

Thank you