It could be due to braxton hicks contraction (false labour pain). It may start as soon as you entered 2nd trimester.
If it feels like cramp, the uterus is becoming hard and the pain last around 30secs, then it probably is braxton hicks. Its the way your body is preparing for the real labour and yes its normal.
If the pain becoming stronger, unbearable, or more regular, then please contact your doctor asap.
You can google it for further reading ☺️
S.