Pre labor?

Kari • Married to my best friend of 7 years and high school sweet heart. So excited that we have our first baby on the way!😍
Having period like cramps. They are consistent for a little over an hour and then go away. Then come back. Been having them like that off and on since yesterday evening. 
This evening they have been a bit stronger and I feel so much pressure I just feel like I have to poop. 
Are these signs of pre labor? And if so how long does it last before real labor kicks in??