Allison: I also agree with Kathryn. You never want to work the same body parts with heavy weights two days in a row. You need at least 48 hours recovery time.
Also, I reduced my heavy lower body to once per week for the same reasons, and then do lots of other lower body work with light weights the rest of the week. I have noticed my knees aren't bothering me as much. I teach cardio/sculpt classes, so for me doing the lower body with less weight happens 5 days per week no matter what. But, for a while I was also doing heavy LB 3 times per week on top of all that. OY, that was too much. So, as a CPT and also fitness instructor I always insist my students not work the same body parts with less than 48 hours recovery. Your muscle fibers need that time to repair. If you were to do S&H three days in a row, your muscles would always be in a breakdown state and you could get injured. Plus it will be harder to see results because it is in the recovery period that the muscle gets repaired and you see the results of your hard work.
Just my 2 Cents!! HTH