A difficult 4km run

I was a day of running today....i started running right from the start of the day.. starting chasing mrt in the morning when going to work... went out for lunch at beach road...i was out at the traffic junction when I saw the bus came to the bus-stop...the light strike red and i sprint down 300m to the next bus stop to catch it i was going home when i spotted my bus coming 200m away...i pick up my feet and sprint down another 300m to catch it reached home late at 7.30pm but i decided to go for a short run.....run is not short for me nowadays..... wanted to do a 4km today...instead of doing loop at the 2km round, i decided to run down to YCK road and U-turn......legs were still heavy from my last run on tues......the first half is a down slope so went a bit too fast.....back 2km was upper slope so i was panting all the way.... finish exhausted....seems like i have ran a 30km 3 mths back....arrrgghhh......need to be consistent to get my fitness back...my tummy has grown and added more stress to my knees.... Shoes: Asics Nimbus VII total distance: 4km total time: 22:26min lap: 2km for 11:26min@5:43min/km 2km for 11:00min@5:30min/km