I know how you feel! I have been dealing with the same since September 23rd! Most of the colds/sinus issues/etc out there are all viral, so there is little we can do medicine wise to help. However, I have a few things that are working GREAT for me!
First, you have a 15-month old!!!!!! And you work!!!! You are probably not getting as much rest as you think you are, and your hormones are still involved! If you are stressed your resistance may be down as well. You are also coming off the Holidays which can take a while to bounce back from.
Does your daughter go to day care or another type of care situation while you are at work? That also may be where your exposures to germs are coming from. I would not go overboard sterilizing your home as we need to build up immunities, but it sounds like you are being consistent about keeping on top of it. Don't forget your car too! This time of year with the windows closed, it can be like a little test tube in there!
Instead of Airborne, I use Arbonne's Get Well Soon supplement. It has a triple echinecea formula and kicks butt! If taken at the first sign of a cold coming on, I usually avoid it. If I take it the first day, I notice that it is usually gone within a few days instead of lingering on.
Your multivitamin may need to be changed too. If it is the one you took prior to having your daughter, it may not be meeting your needs now postpartum.
The other thing I would encourage is exercising through it as much as you can. I think getting out of your routine may also be a factor to your resistance.
I am sick and tired of being sick and tired too and these are the changes that I have made that seem to be working. I hope these suggestions are helpful to you.
Hang in there and let me know if you need a shoulder!