Sorry, a bit gross but please read; I am 3 months pregnant and i went to have a number 2 earlier and when i finished there wass blood on the tissue and the toilet had an iron smell like blood! Am i ok? It's not coming from my V so i guess it's not the baby.
It could just be constipation, or maybe you've developed a haemmoroid if the blood looks 'fresh' (i.e. bright red, fluid). Make sure it's definitely not coming from the front (I know it sounds obvious, but just be sure) and book in to see your GP.
The 'iron' smell is probably due to an iron increase because of your pregancy. Piles are extremely common in pregnant women, and they do 'pop' occasionally (sorry!) but to be safe, have a word with your GP who will have a peepe and make sure all is well.
Makes you wonder how the world got over-populated doesn't it!