Work & pregnancy UK

So im 4+1 weeks pregnant and i told my manager about it, i work a 4 hour shift and i am not entitled to a brake Because its only 4 hours but when i was at work today i felt so hungry it made me feel very unwell, i started having dizziness, i couldn't concentrate at all baring in mind i work in a shop on a till, what do i do when im very hungry when im not allowed a break? I dont want to constantly feel unwell