hi there,
i have a couple ideas for you... first of all, he's probably acting more tired cause he's not sleeping as well. this is likely due to the adjustment in his day -his naps aren't as good cause you're teaching him to sleep in a new way, and that makes nighttime sleep worse, and so on.
once he starts to come around, you will start to see improvement in his tiredness & disposition. keep in mind that it does take time to change old habits - it took you 5 months to get here. if you stay consistent, he will eventually learn. keep in mind too that regression is normal - he will start to get it, and then regress. stay persistant!
i don't think you need to quit bf, but i was thinking that maybe the cereal is disrupting sleep? sometimes, when it's given so late in the day & doesn't digest as well, making them gassy & awake. maybe feed him solids at breakfast & lunch instead of lunch & dinner?
HTH