Good evening, I would be more than happy to assist you today.
It is a very common concern with breatfeeding mothers on whether or not their babies are getting enough, because unlike formula, or milk served by bottle, you can't tell exactly how much your baby is getting. I myself am a breastfeeding mother of twins; and I sincerely urge you to continue to breastfeed your baby, as long as you are physically able to do so. Breastmilk is a lot lighter than formula or cows milk, it is designed to be easily digested by your baby, allowing for all the nutrients of it to be used by baby. Because of this, breastfed babies, especially ones as young as your daughter need to be fed between 8 and 12 (or more) times per 24 hours
You want to be sure that you burp your daughter after each feeding; and you may even want to do so in the middle of each feeding (between switching breasts) to assure that gas is not what is causing her fussiness
Also most importantly, be very conscious of the foods that you eat; as what you consume as a breatsfeeding mother also goes to baby
Drink plenty of water, eat fruits and vegetables (although you may want to stay away from citris or acidy foods) and definitely no caffeine
If you find that none of this helps to change your daughter's fussiness, definitely bring up the concern to her pediatrician at your next visit, as he or she can check for any other health issues that may be the cause of your daughter's fussy behavior.
That sounds like a great idea; keeping a diary. If you do need any further insight or resources, please do not hesitate to ask; I will be more than happy to help.