24wks with a very tight, uncomfortable belly - are these braxton hicks?

[Mimsy2000]

i've had a really tight feeling belly for an hour or so and just feel really huge and uncomfortable. is this tightness braxton hicks? i ate a big lunch but about 4 hours ago so don't think it's that!

i have been getting the same thing for few weeks now - really hard and tight although only for about 5 minutes at a time- midwife says not to worry!