Early run - and can you help?

Sportypal
Check me out - running at 5:30am without any kip! ~2.2 miles in a touch under half an hour isn't bad for me - managed to shave almost 2 mins off my "mile time" too... I'll have that, no bother.

I've got a problem though - the breathing is coming along nicely, I don't get as breathless now which is a definite plus - but my back is fucking killing! Right at the bottom, just above my arse. I'm guessing this is just due to muscle weakness but it's causing me a bit of bother and I keep having to stop (as you can see on the lower 'heartbeat style' graph which measures my speed on the image above. Any suggestions?

Plus I have sore chins but that's because I'm a big fat man bouncing up and down on skinny legs - hopefully it'll settle.

I'd really appreciate some pointers on the back issue though - is it just a case of keeping at it? Should I do less distance for a while?

Cheers