Could be at 37 you are beginning to no longer ovulate.. Which means.. NO RUSH of Progesterone .. which means.... NOT as much thickening of the endometrium lining, therefore... not as much blood to shed...
You won't know for sure if you are ovulating or not unless you chart your monthly cycle and take your temperature upon waking in the morning..
don't go by the kits you buy in the store... they are only as accurate as the as the LH hormone level they track.. in other words, you might ovulate, but if the LH surge in your body isn't up to the kits prescribed level, then it may say you aren't ovulating when in fact you are....
Also, don't go by cramping.. that isn't always accurate either..
Now, your periods are shorter, but as you move closer to PM, you may also begin to notice other changes.. like 2 days heavy, then 5 days lite..
yes yes.. it's the hormones constantly re-adjusting themselves to prepare for the big M................. :)
you could get your hormones checked and see where you are in the "stage"
I am now 49, and looking back, my periods really did begin to change at 37... that is just the beginning...