yes - backing off is a good idea. sometimes we get in such a hurry that their little bodies arent yet ready for it. any time you are faced with a problem like this, take what you've done and back off. maybe its too much too soon.
bananas, rice etc are very constipating. maybe give some more pears, peaches, etc. they need the iron in the cereal, but there is more than just rice cereal. i always bought rice, oatmeal and mixed and my son ate all of them equally well.
around about 7 months you can start him on a sippy cup. see if he will drink pumped breastmilk out of it, (my son wasnt fooled) or just juice mixed with water. as with food, one flavor at a time in case there is a reaction. any citrus juices gave my son a huge rash, but juice will help keep things moving. its all about balance and finding out what you can feed him... and what you cant...
above all, dont be in a hurry! nutritionally, (although doctors will tell you otherwise) they dont need much more than breastmilk for the first YEAR! so dont be concerned if he doesnt eat much solids... as long as he is still nursing, he is getting all the nutrition he needs.. (are you still on a prenatal type vitamin??)
good that you are breastfeeding!! i encourage you to find a local le leche league www.llli.org to support you and encourage you to continue. i am still breastfeeding my 18 month old son and i wouldnt trade the connection and love for anything! so congratulations!! and keep it up! dont get discouraged! if you do - thats what the le leche league can help you with!!