JUST PAIN OR SOMRTHING MORE

So I got my bfp on Monday. Since then in the evenings or early hours of the morning I've been experiencing THE worst cramps!! So tonight I went to see a doctor who said that I could be experiencing Braxton hicks. I've only worked out to be 4-6 weeks. Does this sound right to anyone? I was so scared I was having a miscarriage but seeing the doctor has reassured me as he wasn't worried so I shouldn't be right. He just said if I get any odd discharge or vaginal loss then to get seen again.

Has anybody else experience really sharp lower and I cramps in their first trimester!!? Xxx