Twins without a known family history of twins?

Amanda
At the moment my husband and I are not actively trying to conceive. I had a miscarriage last year and we haven't really healed from it. I'm also fearful that may not be my only miscarriage (given the fertility problems in my family). I will be finished with my degree next year and then we are going revisit the idea of starting a family. 
When I was 18 I went to a psychic on the boardwalk while on vacation with my high school best friend for fun. The woman stared at me for a few minutes then said "you will have twins....boy girl twins and you will marry your high school sweetheart." At the time I didn't have a boyfriend, so I didn't read too much into it. I was more freaked out than anything. 8 years later I married my highschool boyfriend. 
My family has experienced many tragedies within the the past few years so we have been connecting with a well known psychic medium in our neighborhood to help us heal spiritually. In our family reading today she mentioned that new life will continue to come into our family, even after the birth of my sisters little girl (who is due this October). Everyone in our family is a girl.... and every girl has only had girls (so far). I asked the psychic medium if she could see a specific gender, and she said "I see twins, not identical - I see boy/girl twins." It may not be related directly to myself and my immediate family but I am curious of situations in which twins have occurred without any knowledge of twins running on either side of the family. My husband and I cannot think of twins on either sides of our families. I guess twins have to start somewhere. Boy/Girl twins would be awesome. I'm intrigued now that this is the second time I've gotten a prediction that I will have boy/girl twins.
Does anyone else have boy/girl (or b/b, g/g) twins without any knowledge of twins running in their family? I'm curious to see the chances of this happening to myself or one of my sisters. 
Thanks for reading! 
👫