Herbs won't grow properly. Why not?

I am trying to grow chives, oregano, sorrell, sage, parsley, basil, mint, rosemary and thyme indoors. They all seem to germinate OK, but then when they get to a certain size they don't seem to be able to support themselves under their own weight and they lie down on the soil. I am using a peat compost and I did not compress it when I put it in the pots, so it's pretty fluffy in the pots and not too dense. Would this cause the herbs to sag down as they can't establish good roots maybe? The worst offender are the chives and the sorrell, but they are all doing the same thing to one extent or another. Has anyone any idea why they may be doing this? Also, I put all the herbs outside today for a few hours as it was nice and sunny and there was almost no wind, but some of the herbs totally lay down in the soil as if they were vampires or something. What am I doing wrong?