Work troubles...

So I work in a coffee shop which isn't too much strain on me, I told my work I was pregnant the next day just to be on the safe side with the heavy lifting and everything was fine until Friday just gone.

I woke up in the morning with the usual morning sickness constantly feeling sick and I had a sharp one sided pain coming and going so I said to work I wasn't coming in, but that wasn't good enough and got told to come in so I did.. luckily I work with my mum aswell, luckily I got sent home not long after being there, so she phoned 111 and they referred me to my gp who I then rung they said it's just growing and stretching pains and nothing to be worried about. I came back to work on the Sunday and told work what had happened, now the managers are saying they don't believe me and saying I'm not pregnant I cant be stretching this early as I'm nearly 6 weeks, what can I do?