Oh goodness. My first instinct was to say " don't touch the belly", but I've done it before myself with a female with joeys but you have to be very careful. I recommend not to do it too much though and if you do know you could be risking the joeys life. You see if the joey gets unlodged from the female usually its jaw gets broken and until they are very far along they can't unlatch and latch to the teat on their own.
After the joey is in the pouch for about two weeks you should be able to see the lump. It takes roughly 16 days after conception that it crawls into the pouch, so wait a little while longer.