Need some advice

So ive had this "balling up" feeling in my stomach and sometimes i just rub her and she streches out. I told my doctor and she said if the baby does this more then 5 times in an hour that it could be preterm labor( i freaked out and now constantly counting) i have no bleeding and no leaks as the doctor put it . it seems to happen alot when im laying on my back. Any of you ladies had this? Btw this is my second baby girl and the last time i was pregnant was 10 years ago. Currently 28 weeks💛💙💜❤ Due march 13🍀