Hello Barbara,
Breastfeeding is challenging for a working mom but there are some tricks of the trade so to speak that can help you. One suggestion I can make is to try hand expression instead of pumping, every chance you get. You can do it in the bathroom. Take 2 minutes to empty your breasts and put the milk in a cooler with an icepack. You can get a "soft bag" in black that looks like a purse and keep it with you as you run around putting out fires in the office. If you can find a way to pump at lunchtime or just before you leave the office, great. If you hand express while at work it will keep your milk supply going
My next suggestion is that your 4 1/2 month old doesn't necessarily have to breastfeed on a conventional schedule. Many working moms breastfeed as much as they can while they are home. You can be as creative as you like with this. You can breastfeed all evening, and once in the night and when you wake up. This way you can spend all evening with your precious angel and part of the night. You'd be amazed at how many hours per day with your baby that this works out to. If you find your baby refusing to breastfeed, get into the bath with her. Skin to skin contact is fabulous for reconnecting.
Have you used a supplementer at the breast? This is a wonderful way to keep your baby breastfeeding while supplementing with either your pumped breastmilk or formula. You're baby only needs about 1/2 oz of breastmilk per feeding to get all the immune benefits.
There are herbs that you can take to help you with your milk supply. If you go to the breastfeeding section of this site and look at the Newman-Goldfarb protocols, the herbs are there. Lenore recommends fenugreek and blessed thistle in combination. They worked quite well for me.
You probably feel like breastfeeding will never end but you're only 1 1/2 months away from your baby starting solids. Once that happens, you're baby's need for breastmilk will diminish anyway. In the meantime, Why should you miss out on all the fun parts of being a mommy?
You know these are very important months for you and your baby to spend together. They grow up so quickly. Get as much time in as you can. The bonding that you do now will help you later when you child is older and you have to spend time at the office. You'll always have this unique intimacy that only you and your daughter share. And the gift you're giving will last her whole life.
Try to find the strength to go on breastfeeding just a little longer. You won't regret it.
Esther