How many is too many Braxton hicks contractions?

I'm 30 weeks currently. last night, I had Braxton hicks (not painful, just tight) every 2 to 3 minutes that lasted between 30 seconds and a minute. this lasted for a few hours. I showered, ate, drank a lot of water, and laid down. it took another hour or two, but they slowed to 6 to 7 minutes. Since they weren't painful, I just went to bed. I've only had two since I woke up this morning, and I've been having between 10 and 20 a day, so today is normal. I did email my doctor just to let her know and ask her what she would like me to do if it happens again. This is my second baby. My soon to be 5 year old was born at over 41 weeks, and I had been dilating and contracting since 35 with her. That's why I wasn't worried last night, however I'm only 30 with this one. Has anyone had them regularly like that and it was nothing as Well? I know I did way too much physical activity yesterday, so I'm going to be careful now after that. Anyone else have anything similar? Anyone actually in end up in preterm labor and not know at first?