How many braxton hicks is too many??

I'm 35 weeks pregnant and the last few days I have been experiencing more and more braxton hicks. And iv been noticing them more because they are getting more uncomfortable. They are happening more frequently. I have read if you have more than 2 an hour to speak to a midwife. Iv been experiencing much more than that, maybe 6/7?? I have been having a lot more back pain and lots of pressure to the point I can't walk far at all? So when do you need to start worrying about ore term labour? What are symptoms of it??