Hi Tat2ed---I should start by saying that I don't have any suggestions about relactating, except to say that if you want to do it then why not. Human breast milk is best for babies.
Don't worry about your little one not doing well on cows milk. His body is trying to tell you something. Cows milk is NOT a healthy food for humans. It is one of the mostly highly allergenic substances for humans. Unfortunately, these allergies are usually not attributed directly to diary AND our wonderful gov't has the USDA, a dept set up to promote American agriculture...good or bad.
But don't take my word for it. Please go to www.pcrm.org and put diary in the search box. Other good source for info are www.thechinastudy.com and www.notmilk.com. I say these things as a reformed milk drinker having quit after taking a series of wellness classes taught by a Naturopath who has her PhD in Nutrition. The science is clear, it's just not well-known. Please feel free to contact me if you have any additional ?'s about any points that I've raised.
And, another thought about relactating...your success will depend, in part, on your diet. Be sure you are eating mostly fresh fruits and veggies, whole grains, legumes/beans, nuts and seeds. Supplementation is usually not necessary when you eat this way, but I do think that a high quality WHOLE FOOD supplement is beneficial as nutrition insurance. There are HUGE differences between supplemental food and isolated man-made vitamin supplements. Look for one backed by independent research. Again, I have great info you can use to make an informed decision.
Good luck with whatever you do. Be well, D.