Why am I not Sore?

I find this very discouraging. I feel like I'm not doing something right. I've gone up in weight but my legs are no longer getting sore.
When you first start lifting, almost every exercise will produce delayed onset muscle soreness (DOMS) in the effected area. Over time, the body adapts and this soreness is reduced, sometimes eliminated altogether. That does not mean that you are not still growing and getting stronger, as evidenced by your progress. Don't be discouraged. If the weights keep climbing and your mass keeps increasing, keep at it.


Often, you will find that if you make change to your routine, i.e. change exercises, rep speed, volume, etc., you will once again experience acute soreness, but it will dissipate more quickly than during that first phase of adaptation. Also, any layoff, even a couple of extra days, often produces a resurgence in muscle soreness.

Over time, you'll be able to use soreness to gauge what muscles or parts of muscles a new exercise is targeting and if a new exercise protocol is stressing your physique in a new way.
You'll also find that different muscle have different delays and responses in when and how sore they will get.
Interestingly, DOMS is most often attributed to eccentric muscle contractions. Lowering the weight seems to cause more micro trauma in the contractile fibers.