Back pain?

Chelsea • Baby 3 due April 2017 ❤️
I feel like I've posted a million things lately, sorry lol. I'm so much more worried this time around than I was with my son, anyways, I went grocery shopping tonight and after we got home my low back is killing me. I'm only 4.3 so I highly doubt walking around this early will give me issues but I honestly can't help thinking I'm going to miscarrying at any moment, anything I do is going to cause it :( 
Is it normal to get low back pain after walking around a lot? I was wearing slipper because I dealt with 2 toddlers today and at the end of the day I was out of fucks to give lol.