Okay week 5... play it real differently then!
First off, the plants might benefit quite a bit from a larger home. The new soil should be light with GREAT drainage to prevent overwatering and maximize oxygen to the roots at this very important time in bud development.
Next, late in flowering, yellowing low leaves is not uncommon or even undesirable. You have ~3 weeks to go if you are running an average indoor strain, and that is about what I'd expect to see.
So my advice:
Larger pot with good drainage, fresh light soil, and as for fertilizing, keep doing what you're doing. Let the soil dry out a bit between waterings too.