I have used papain with some marinades for goat meat. Personally I do not care much for marinades any more, at least not long ones. For example, I used to marinate chicken overnight with spices and yogurt when making chicken tikka or tandoori chicken.
1 Pain at the base of the spine causes the psoas muscle to shorten and weaken(1,2,3,). 2  80% of Western people will suffer from debilitating backpain some time in their lives(5).  Western style walking (comfortable shoes & flat ground) fails to trigger muscles that stabilize hip joints & lower back.
The lump at the base of the neck that is hard could be a lymph node, a cyst, a neurofibroma or harmless collection of nerves and fibers. Since it has been there for three years and not growing, any one of these could be a possibility. However it could also be an abnormal spine curvature if you feel it that way.