Due any day and back ACHES

For about 3-4 days now I've been having dull period like cramps. But yesterday morning I woke up and had just a constant ache in my lower back. Not like being strained from being pregnant or anything like that, it feels internal if that makes sense. It just really aches bad but with no pattern. This morning it's still happening and feels a little worse. It's not as bad when I'm up and about but the second I lay down it's extremely uncomfortable. Has anyone ever experienced this right before labor??