Hi, just wondering what the difference is between Irritable Uterus and Braxton Hicks?

The reason I ask is because in my last PG, I experienced excruciatingly painful runs of BHs from 37 weeks onwards (none of the info I read indicated that level of pain is 'normal' for BHs). Now, for the last month or so (I'm 27 weeks) i've been having very strong BH sensations that are becoming increasingly uncomfortable. They are strong enough to affect the way I walk and seem to be quite frequent.

I have asked the DR about this and she just said if it becomes really painful then you are in labour and need to go to the hospital... which is not a reassuring answer. Where's the line between "normal" BH and Irritable Uterus - is it based on strength, or frequency or duration of contractions?