thanks guys,
I am already eating store brought skim yoghurt, but as this is the only thing I can eat these days,I could consume half a kilo a day but can't eat any thing else and home made yoghurt is a lot cheaper, two kilos of yoghurt just 2.5$ isn't it great.
to every one who wants to make it at home, make it in a flask which keep the mixture warm for few hours.