Sounds to me that the best thing you could do is try and get another 2 hours at work or as someone else said, see if you can do 2 hours of ironing or ANYTHING for someone so it counts as 2 hours work. Working tax credts and family tax credits are fantastic and have saved me! I am ona decent standard of living becasue of them. You get free school meals and other benefits - medical, dental etc. And council tax. I have also just ehard from my gas/electric supplier and my d debit has just been reduced from £127 pm to £36 - shows just how much XH was costing us int hat department!!! Check with IR and see if you can count voluntray work in your 16 hours, then you could ask if you could pop into your local school and listen to readers for a couple of hours a week. Anything to get to that magical 16!!!
And re your GP - go and see him. They see this all the time and you sound like you are a great mum!
take care and good luck!