At 5 months (APA recommends starting solids at 6 months), you are just trying to introduce solids, not try to supplement diet. This should by any means be providing him any nutritional value. For the 1st year of a baby's life, breastmilk or formula is all he needs. I did not start solid with my daughter until she was 6 months and I started off a few times a week for at least a month before I tried any more. They are now saying that some cereals may not be the best first foods either. You could try some veggies or fruit too (mashed bananas and avocados are great). I always nursed my daughter first before offering her any solids.
Why cause yourself added stress when you don't need to. Best of luck to you!
~Annie