morning pain almost gone by evening

I don't know if this is RA, fibromyalgiaor PMR but in the morning I am so stiff and sore I can barely get out of bed and get ready for the day. We go t the gym three days a week where I do weight machines and cardio machines and take a nap when we get home. On the days we don't go to the gym, I just putz around the house, read, play on the computer and take naps. Since I can't take anti-inflammatories anymore because of blood thinners, the rheumatologist and I haven't found any thing except steroids that control the pain consistently and they don't last all that long. The odd thing about all of this is that by late afternoon, the pain is subsiding and is almost gone by bedtime, regardless of what I do or don't do during the day (even if I sleep most of the day.) Has anyone else had this experience? Is there an explanation for this?