K.Y.
Spotting is always scary. I've had experience with spotting during the 1st trimester. This last time we think it was due to an "absorbed twin." This is where there is a second embryo that is fertilized and multiplying but doesn't implant. It all stopped by the end of the trimester and the other embryo was absolutely fine. Today, I have a beautiful 4 month old son! Stay positive and follow the advice of your OB. You'll be in my prayers.
P.S. I'm an older mom too.