Hi,
You mentioned making diet changes.. Were you taking a lot of fiber?
Too much fiber and not enough water can cause constipation.
There is an obvious correlation between your diet/activity and appearance of symptoms..
Being constipated for a some time now, you may have developed fissures hemorrhoids.
Next Steps
Increase water intake to 3 liters a day
Stop synthetic fiber and take natural ones in fruits and veges.
As you are bleeding, it is time to consider laxatives to prevent further bleed.
Health Tips
If the bleed is more than a teaspoon, see a doctor asap.