Speak to a union
I think the charity pregnant then screwed have an advice line for work stuff x
Do you have an employee handbook? That should explain how to make a complaint at your particular work place. ( look for grievance policy or complaints procedure) Also in the first instance I would address this directly with your manager and explain what has happened and that in future you will need to attend to get medical care immediately. I would put this in writing via email if possible after first discussing in person.
I think you could talk to a company called ACAS, they deal with employment law. Sorry this has happened to you!