I wonder if you have heat damage? If you consistently pressed your hair every week for 6 years, over time your hair probably stretched out a bit. Now that you've stopped pressing, your stretched out hair may be breaking where it meets the new growth. This is only a guess of course...
Also keep in mind that shedding is normal, especially if you're wearing protective styles. The hair that would have shed daily if you were styling each day, comes out all at once while you're detangling and washing.
Don't be discouraged! The amount of shedding you're experiencing may not be as bad as you think. I hope this helps!