When he poops, is it normal, soft consistency, or is it hard? Both my kids, although they were breastfed at the time, would only go once a week when they were that age. My son even went TEN DAYS without pooping when he was about a month old. When they finally went, it was soft (and sometimes a BIG mess!). My doctor explained that their bodies were simply using most of the food they were taking in, which is why they didn't need to poop more than once a week. He told me not to worry and not to do anything about it. As they got older, they began to go more frequently. I have noticed that different doctors have different opinions, that's for sure!
If he's constipated and his poops are coming out hard when he finally goes, then we're talking about a different situation. I would definitely check with your doctor's office before trying anything on your own with a 10 week old.
Hope this helps.
-A.