If you want facts, go to www.bettysplendens.com
Read through these and other sites as well as the stickies here, you can also ask for help like you are doing now.
Your feeding is not enough. You should be feeding betta pellets (minimum of the first two ingredients have to be protein and it has to have a minimum of 40% protien). Most freeze dried foods are the fish equivalent of potatoe chips or fatty french fries. Flakes are messy and not really as nutritous as pellets.
If you are doing partial changes, you are doing a fish in cycle. If so, you must have a filter in that 5 gallon running 24/7 with filter media that'll stay in there all the time. You can clean the filter media by rinsing it out once a month in old tank water. In a 5 gallon with ONE fish, you have to do 50% water changes a week. In the five gallon (if it doesn't have a filter), you should be doing two 25% ever week and a 100% every other.