Stretchmarks are most likely to crop up on your tummy, breasts and thighs from about six months onwards. They're the outward sign of broken elastic fibres in the skin and look red at first, but fade to silver-grey. There are creams and gels that claim to reduce their effects, but they can't do that much as the breaking of the fibres occurs some way beneath the skin's surface. The tendency to stretchmarks seems to run in families, so if your mum got them, you're more likely to get them too.
Your hair
Hair can look shiny and thick in pregnancy, probably because normal daily hair loss slows down. After the birth you may feel as though your hair's falling out more quickly. It's probably the contrast you're noticing, rather than anything more serious, but speak to your doctor if you're worried.
It's fine to use hair colourants and perm lotions on your hair, although you may find the results are unforeseen.