Most likely you are just becoming tolerant to your dose and that's why it's losing it's effectiveness. You could ask for an increase. Its normal for you to need a dose increase or few when you first start stimulants to find the right dose for you.

As for the depression, honestly stimulants can exacerbate that as well as anxiety. However, your tolerance to the Focalin could be making you feel down. So ask your doctor to bump up your dose as long as you're not having any other side effects from it.

Good luck!