welcome to HCM,
congratulations for reaching up to 33 wks of pregnancy
with out any complication.
madam what you are experiencing is commonly seen in 32 to 36 weeks of pregnancy and are known as pressure symptoms, due to the increasing size of uterus
, which reaches its maximum in these weeks.
don't worry these pressure symptoms will subside very soon, as the fetus will start moving in to the pelvis .
presently to take care of yourself and the pain, do not suddenly change your position or posture, rather do it slowly.
i suppose sitting position must be more comfortable for you then a complete straight lying down.
take care of yourself and may god bless you.