I was never officially diagnosed with an irritable uterus, but did spend from just before 26 weeks until Tristan was born at 34+3 experiencing irregular contractions, tightenings and BH's. At 26+2 I went into threatned pre-term labour, which they thankfully stopped from progressing.

My advice is to trust your instinct, no-one knows your body like yourself and if you feel that something is wrong, dont wait go straight to the hospital, at least for peace of mind!

Also if you get tightenings along with back pain it'd be a good idea to at least contact your hospital. That can be a sign of pre-term labour.