I am 23 weeks pregnant and I feel contractions, what should I do?

Hi, I am 23 weeks pregnant. I started to feel contractions in my vagina, then sometimes my belly hardens in the bottom, sometimes not. It's accompanied by menstrual stomach aches. It's not regular or frequent (4x/ day for the past 2 days). I was wondering if these could be false contractions, if I should be worried, etc. How can I be sure that they are false contractions? Is it normal to really feel contractions in the vagina:15-20 seconds