I'm probably just freaking myself out...

I have had multiple miscarriages last year, one around this exact same time. I just found out I am pregnant again. I had a lot of cramping last week, went in and they did an ultrasound. Everything looked great. We saw the heartbeat, beating right around 122, measuring right at 6 weeks. Today, I am having more cramping, but no bleeding. Just like really intense cramps and lower back pain. But they said everything looks good. Did anyone else experience such intense pain? I am probably just experiencing some mild PTSD surrounding this time of the year from everything that started last year at this time. I thought seeing that heartbeat on Friday would put me at ease, but feeling the cramping just makes me so nervous!