How is time going so fast?!

Today, my baby is 5 months old. I have no idea how because it feels like she just came out of me yesterday. The funny thing about having a baby is that they feel brand new and like time's going fast really quickly, but at the same time it's hard to remember what life was like before them.
Every day, she manages to astound me. For example, today she sat up by herself for a good 6-7 seconds whilst holding her arms out like a tightrope walker, instead of the normal hands on the ground to prop her up. She also pushed herself right up to the crawling position so, considering how adept she is now with the tummy shuffle, I should probably start baby-proofing quite sharpish!
My theory on why time seems to go so quickly is that you spend your whole time blinkered and focussing on getting through the day, so you don't actually notice that getting through the first few days has become getting through the first few weeks and then turns into getting through the first few months. Well, that kind of makes sense in my head.
On a bad note, I think that the lack of rest and lack of time to express milk is finally having a knock-on effect on my supply, so I'm going to try to ease up on the exercise a bit and make more time for expressing. I've been trying to do at least 40 minutes of exercise a day, not including walking or my weekly zumba class. That might not seem a lot, but when you combine it with breast feeding, doing 99% of the parenting and 2 night feeds, it's actually quite knackering. Especially as I normally end up doing at least half of my daily exercising after 11pm as we don't normally have dinner before 9pm and all my time prior to that is doing mummy stuff. Any time after dinner should be chocolate and TV chilling out time, not sweating to some chirpy American woman telling me to feel the burn time!
Isabella has 1 more month before I can start gradually introducing lumps and more foods, such as lentils and small amounts of cheese. It's really exciting in a strange way! I'm going to be researching some nice recipes that I can try out on her.
I'm going to try to squeeze out some more booby juice!
TTFN x