When i had lab work, my myoglobin was flagged as low (less than 22) i also have stiffness/pain in joints. should i be concerned about ra?

Not because but....: Low myoglobin is not a regular diagnostic test for rheumatoid arthritis at all. It also can be lower due to other diseases or scenarios BUT joint pains and specially morning stiffness for more than 6 weeks YES are of concern to suspect rheumatoid arthritis ( RA). RA is a chronic autoimmune inflammatory arthritis that usually affects the smaller joints in the hands and feet.