I'm Not Teezee.. but I may have some helpfull tips for you.
First I'd suggest you drop the cereal until you have night sleeping figured out. 4.5 months is really early to start.
then shorten the time your LO is awake first thing in the AM, 2 hours may be to long. Get your LO down by 8-8:30am and try pat/shush to extend naps.
Start with quieter activities first thing in the AM like mat time or tummy time and the Jumper or saucer in the afternoon, so more energy is used in the PM. try for no more then 1.5 hours of wake time to start. You LO may be overtired and thats why he's only having short naps.
Move bedtime to 7pm with a steady routine starting at about 6:30pm. Use only quiet activities like massage and reading. Don't use the saucer or jumper as they'll overstimulate your LO making sleep time harder.
Try getting a dreamfeed in at about 10:30 if your LO hasn't woken.
When he wont sleep try pat/shush or PU/PD to settle not the swing as that will become a prop.
Try a routine similar to
7am wake eat
7:30 activity
8:30 nap
10:30 wake (if hungry feed if no light activity like reading or singing)
11 eat.
11:30 Activity
12:30 nap
2:30 wake (if hungry feed if not light activity)
3 feed
3:30 activity
4:30 cat nap (no more then 45 minutes)
5:15 light activity (you can throw in a cluster feed here too)
6:15-6:30 (depending on babies mood) Start bedtime routine.
a good one is Bath, reading singing or massage (only one as all 3 would over stimulate) then feed
7pm bed for the night
10:30 dreamfeed
then if your LO wake in the night use pat/shush or PU/PD to settle.
One note however is that if your LO is not fussing don't try either PU/PD or pat/shush. Let him learn to settle himself. The key is consistency. If your LO is playing I know its hard to sleep but if you go to him you'll only make it worse. Given a few days to learn to settle he'll start to do so and will resume sleeping on his own.
Adjust this routine to your life and needs. Its a flexable routine but its a solid one.
HTH