How long does watermelon keep?!

How long does watermelon keep?

I just cut a watermelon that ive had for maybe three to four weeks. The outside is still green and hard and the inside looks fine. I took a bite and im not sure if it tastes funny or if im paranoid.

19 hours ago
I just cut it open. It was not already cut. I just opened it.

From the moment it is available in the markets - Sell by dates are approx 2 weeks. Left whole in low temperatures they might last longer.
They do ripen with age.
Placing them in the sun even after picking they continue to develop.
If you place them in the fridge then their growth is heeded.

If you cut off a slice and eat it and forget the rest for over a week the taste might be different as its no longer fresh like.

Check for any and all dis-coloring before tasting.