Hi Stary,
While I don't want to worry you unnecessarily, I would try and see if you can get your DS scanned as soon as possible (ultrasound and/or x ray). Uneven leg creases can be a sign of hip joint problems. Now the chances are that there is absolutely no problem at all - not all babies with uneven creases have dislocated hips. But if there is a problem, you are still at the stage where it could be rectified relatively easily, whereas if it is only picked up later, then the treatment options are much more limited and much more invasive.
My 5 month old DD has DDH, developmental dysplasia of the hip. Her hip isn't dislocated as such, but the socket didn't form properly, most likely due to her being in breech position (was your DS in breech position - this is a risk factor?) The problem was picked up by a scan at 14 weeks and she is spending 12 weeks in a body harness. This is far less drastic than it sounds! It was a bit rough when the harness first when on as it restricts her leg movement but she soon got used to it and it's been absolutely fine since. It should come off in 5 weeks time as the signs are it has worked OK. But - her problem was not picked up at any of her checks by health visitors or doctors, both of which examined her hips and said they were fine. It was only discovered at a routine ultrasound scan carried out because she was in breech position.
It's extremely unlikely your DS has the same problem - it's much more common in girls than boys for some reason. However, just on the off chance that he does, it really is worth finding out now rather than later - as I say treatment at this stage is much much easier than when they have started walking. In the very unlikely event you do end up with a harness, I promise you it really isn't very difficult to cope with. Post again and I'll give you lots of tips.
Good luck - and remember it is very unlikely that you have anything at all to worry about, especially as you have a boy rather than a girl.