It is not unusual to get this problem at 29 weeks. It is caused by your increased blood supply and the reduction in blood return to your heart (caused by the size/weight of your growing baby).
Just to add to yogababy’s suggestion you could try is to sleep with your legs/feet higher than your heart. To do this you can put some rolled up towels/blankets under the mattress or even put the legs of the bed on some Woden blocks. Also do not sleep on your back. Hope this helps to give you some relief.