oic, register your 2nd one for childcare and if no vacancy, see whether nearby has playgroup so you can a breather of 2 to 3 hrs per day. If childcare has no vacancy, register 2nd one under waitlist for all the childcare center that are convenient for you. That what I did for my first one and I waited for 18 mths till she got a place as I live in Jurong west so there is a long waiting list for childcare.
Since you are not working, remember to apply for the additional childcare subsidies when your 2nd one got in childcare.
Bring your baby and 2nd one to downstairs and stroll around if you can manage. The 2nd one can play around in the playground, you can watch over. This way you wont be trapped between fetching your kid from school and home.
Tell yourself, you are not trapped , this arrangement is only temporary. Once your 2nd one enroll into childcare, you will manage better with your baby. When your baby is older or when you find a suitable baby sitter near to you, then you can better plan for your future. My suggestion to find auntie in your block is such that it save time and when it rain, its easier for you to send and fetch the baby. Same applies to your 2nd one if you can find childcare close to your home.
Better find a job after you feel better and less stess else you will feel more stress in managing your job and 3 kids especially if you need to fetch them and feed them.