At least you did receive some colostrum from your mother, which is chock full of antibodies and many immunoresponsive factors. Breastfeeding is extraordinarily important to immune system function in children, and perhaps throughout life.
It is certain that amongst the most important breastmilk is the very first few days, as that is when the initial immune system assets are primarily passed to infants.
You are clearly applying sound thinking to the questions, and I am sure you are better informed than I ever could be about your medical situation.