I was pregnant, and I am now at 13 weeks. This can happen at any time. I have no control over this. I'm afraid it will cause a miscarriage. Orgasms are unlikely to cause a miscarriage.
Most people only have orgasms with actual intercourse or clitoral stimulation.
Some women will orgasm out of the blue. This may be more common in pregnancy due to increased blood flow to the vagina and clitoris. Sometimes, with a prior history of miscarriage, especially if there is cramping or spotting in the current pregnancy, we recommend avoiding sex. Your doctor will know best given your individual situation. Blood pressure tends to drop in pregnancy.