My 4 wk old did this, too, in the first couple of weeks.
I continued to offer her the unfavored breast and let her nurse there until she spit it out, then latched her on the other side for about 5 minutes, then switched her back to the unfavored breast. She ultimately evened out her preference and began nursing pretty steadily from each side.
I think it's just a comfort thing maybe? Because I was worried that the milk flow from the unfavored breast was slow or non-existant, so I pulled out the manual pump to make sure the milk was flowing, and it was...so once I was reassured on that front, I just sort of let her work it out.
I continued to offer her the unfavored breast and let her nurse there until she spit it out, then latched her on the other side for about 5 minutes, then switched her back to the unfavored breast. She ultimately evened out her preference and began nursing pretty steadily from each side.
I think it's just a comfort thing maybe? Because I was worried that the milk flow from the unfavored breast was slow or non-existant, so I pulled out the manual pump to make sure the milk was flowing, and it was...so once I was reassured on that front, I just sort of let her work it out.