Your back pain
and difficulty in breathing can be due to stretching of the abdomen as you are carrying your first baby and the weight of the uterus
pressing on the spine. False contractions are common at this stage of pregnancy
. You can put up a back rest when you lie down to make you breathe easily.You will know when your baby descends by frequency of urination, excessive vaginal discharge
sometimes reddish , low back ache and pain along the hips and reduced major fetal movements as you can feel the head fixed over your pubic region in case of normal presentation. Have a regular followup with your doctor. Wish you a healthy delivery.