You have allowed people to overstep your boundaries of generosity and they have exploited your kindness.
Being used, manipulated, or dominated, or sacrificing your own needs to assist others, can be physically reflected in your immune system. Circumstances and environments in which you give too much of yourself will generally weaken your immunity and break down your protective layers.
Emotions arising from intimidation, emotional and physical abuse, criticism, bullying, harassment, inner conflict, and oppressive environments can also be associated with low immunity. Redefine your boundaries, lower your tolerance, and actively make changes that will help rebuild your body’s physical and emotional defenses.