I completely agree with the previous poster re-comfort as a possible reason and the benefits of extra expressing and with the comment that
solids must be your last resort.
What we often forget is how rich breastmilk is in calories compared to so many other foods:
breastmilk - an average of 22 calories per oz.
apple sauce: 13
rice cereal: 20
pears: 16
carrots: 7
It simply isn't the case that at your LO's age she will be able to absorb calories from her solid foods that are superior to breastmilk.
If you are exclusively breastfeeding (feel for those mums who would desperately wish to be in your position) there are good reasons to hang on and look at other ways to solve this problem - this is because of the way breastmilk coats the lining of the baby's 'open' intestinal wall preventing the the passage of pathogens and allergens into the bloodstream. If you add solid food to this environment the coating is compromised. A baby's gut doesn't tend to 'close' until nearer 6 months. The decision when to start solids is obviously a personal one that each family must take. Some people feel strongly that their babies are curious about food and want to begin, some people are advised by their doctors that they
need to begin solids e.g in the case of reflux.
Feeling unwell and going back to work are all things that might have affected your supply. I would work on that first. Even if you
did add solids at this age you would still need to ensure any potential supply problems are ironed out if you feel that is what it might be - solids for young babies is more about 'experience' and tastes than 'filling up'.
Is it also possible she may be going through a growth spurt or a new developmental stage? It is tricky to meet the needs of a growth spurt when you are working. I would try some extra pumping as suggested and perhaps consider taking a supplement that might help boost your pumping output e.g. fenugreek.