Stomach keeps cramping

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I'll be 19 weeks this Wednesday. I keep getting sharp cramps on my right side of stomach. Just for like a few seconds and then it goes away. I'm not spotting at all either. How do you know when it's serious enough to go to the doctor? I rarely feel baby move but when I push down a little- I can feel a heart beat in my belly. I think it's just normal pains but I want to make sure it's normal. My last child was over 8 years ago and I don't remember any of this part. LOL