I don't think thats alot of shedding either
If your hair is feeling spongey and weak to the point of breakage- that may be an indication that you may need to increase the protein in your regimen. The protein will give your hair more structure and help it be able to better withstand breakage. Seems like you've simply done too well a job of moisturizing
balance it with a mild protein treatment. If you don't want to do a full blown protein treatment, you can just use a protein based moisturizer until you are able to wash.
When my hair does this, I find that the Cantu Shea Butter Break cure and growstrong really do a good job of strengthening the strands when I've overdone the moisture.