cramps at 18 weeks

Hi was just wondering if it was normal to feel cramps at this stage. I have been having them all day and had some last night. They are not painful but they have been continous feels like I'm starting a mild period. I haven't done anything today since I'm off so not straining myself. Also no bleeding at all just discharge and it's normal. I'm really scared but keeping as calm as I can. Should I call my doctor? Or is this normal?