Generally speaking, constipation isn't usually an effect from spatone as the iron in it is very readily available to be absorbed by the body without causing side-effects... It's possible, if you are constipated that it's just general pregnancy sluggishness that so many of us are afflicted with thanks to hormones!
Either way, tackling it is the same whichever the cause. To increase fibre and increase fluids usually does the trick. Some gentle exercise (just walking will do) may also have a positive effect.
Hope you 'go' soon 