stretch marks questions

I am 37 weeks. My belly has always been hard and I have developed a couple of stretch marks on the lower part of my belly.  They aren't very red but they are there.  The baby is now head down/dropped.  I notice that my lower belly now feels flabby where the stretch marks are and the upper part of my belly is harder.  I told my husband that I thought it was maybe because the baby's butt and legs take up more space.. he said he thought the head and shoulders would take up more space.. hmm  Can anyone explain this?