I have the same problem. My DD is almost 10 weeks and only feeds from one side for about 10 minutes. It worries me that she's not getting enough but she's consistently gaining the 5-7 ounces a week my lactation consultant recommended.
As long as LO is gaining the right amount of weight, I wouldn't worry too much.
Also, I have found that feeding from one side at a time per feeding session is okay for overactive letdown mom's like us. It helps the baby get all of the fore and hindmilk.
My Angel Baby -- BFP 12/28/10, EDD 09/07/11, D&C 02/28/11 -- I miss you everyday!
You are doing everything right. My baby is 13 weeks ans just now we are feeding both sides. He can handle the forceful letdown so much better now that he is bigger.