Contractions only when you lay down?

Ar

Hi! I’m 39 weeks and 4cm dilated for the past 4 days now. I have felt strong painless contractions for a week now. However, they seem to come on the longest when I lay on my back (not 100% flat, but definitely not upright with my pelvis facing the floor). Does anyone else have the same thing happening to them? I’ve always been under the impression that walking or sitting on a yoga ball stimulates contractions but I feel like exercise stops mine. Anyone else feel like this?