How to know if you are having contractions? (1st preg)

jennifer 👶🏼👶🏼
hi, so i have looked everywhere in the app and i dont see any posts regarding contractions.  I wish there was a tab for it  lol.  I looked under first  time moms and no one really asks what contractions are like,  at least not as far i scrolled down to look.  Not only is this my first pregnancy but im also having twins.  And because your  body  goes thru so many changes, theres many different things that we feel and experience and some ive noticed that singleton moms dont even go thru or have.  
In several occasions i have woken up with pain, and so i just try to figure out what it is and its like a guessing game every time.  First it was a sharp back pain that went away when i got up to go to the bathroom.  This morning i had a stomach ache that woke me up at 5am, plus my belly was hard and my stomach was making a lot of noise. both times first thing i do is llok at the time to keep track of it in case they could be contractions.  im just scared that i end up having them and i wont know that they were!!! 
sorry for such a long story!! and your experiences are are welcome!  😊