Auto generate next number for selected criteria

Hello brilliant people! I am trying to auto-generate protocol numbers. Our layout is simple: current year, type of doc, then a sequential number. Ex: 2015-IQ-001. I need a formula that will create the protocol number by using the type of doc and adding the sequential number. So, if I have -001, then the next IQ doc would get -002. If they choose type PQ, then it would get 2015-PQ-001, then -002 etc.

They may choose a type by a drop down list. I can get the "2015" and the type, but I do not know how to get the sequential number set up. I'm sure it's some kind of COUNTIF and +1 kind of thing, but I just can't figure it out. Please see the attached file for further explanation.
Auto gen Protocol numbers.xlsx

PERFECT! I love you guys! Thank you so much!

Catniption, the formula for number sequencing is:

=COUNTIF($D$2:D2,D2) for cell d2 and copy down for the rest.

Edit: see my post was delayed here!