Thanks for your query to health care magic.
As per your dates, you are in your third trimester of pregnancy
and reached term (after 37 weeks, we call it full term pregnancy) which means your baby is ready to see this world anytime.
And during this period , your baby's head gets fixed (ie baby's head has dropped into the mother's pelvis), and this is the cause for the pressure you are describing, also you will notice that you are hitting the urinals very often.( due to the pressure of baby's head on urinary bladder
the heaviness in lower abdomen and tightening you are experiencing is known as Braxton Hicks contractions(false labor pains) which are usually painless and expressed as a' tightening' sensation
As you have reached term , my advice to you is,
Watch for signs of labor- False labor pains usually concentrate in the lower abdomen and groin, while true labor pains may start in the lower back and may spread through the entire abdomen. Real labor also becomes stronger and more powerful as time passes.
also report to a obstetrician immediately if you have any of the following:
-blood-stained mucous discharge from your vagina.
-Your contractions are about 5 minutes apart, or
-You no longer feel comfortable being at home, or
-Your waters break.
Hope the information was useful.