Stomach gets hard randomly

I'm six mos along and latley I will wake up at night due to discomfort. I can't find a good position to sleep in and my stomach feels so hard like it's gonna bust open. I thought it was the baby pushing out against my belly but read somewhere it could be Braxton hicks contraction. It is very uncomfortable, not painful in any way, just makes my tummy so unbelievable tight feeling. Sometimes it makes me have to go to the bathroom ( number 2, sorry tmi) and then it will relieve a just a bit.  Overall the hard tummy can last 5-25 minutes. Anyone else have this situation??