Horrible period-like pains at 14 weeks pregnant

Natalie • Pregnant with my third baby :) couldn't be happier. Roll on August 2016!
I'm 14 weeks and three days pregnant to this day (to be precise) and I've been having horrible back ache and belly ache which feels like I'm about to have a really heavy period. 
I don't remember having this with my first two children. But it's slightly worrying me.
Thought the best place to get some advice would be from the mummies on here!
Any reassurance/help will be gratefully received.
Thank you in advance x