Constipation can be a cause, but if i remember right i think the hormones that tell our muscles to relax so our bumps can grow are also a big cause. Our blood volume is increasing which already puts stress on the veins, along with relaxed muscles and everything means that any weak spots are vulnerable. In your bottom this means hemorrhoids, (veins that swell) and everywhere else they're called varicose veins. I was lucky not to have them in my first pregnancy til a few weeks before birth, but this time got them at 6 weeks. On the upside after my sons birth they disappeared and stayed away completely til this pregnancy so hoping they will vanish again after this one too x