Does anyone have any idea what's happening to my capsicum plant and what I should do about it? There are no visible bugs on the leaves.
Is it in vase or directly on ground? If you have only one and it's in vase, I suggest to take it away, clean the roots, and replant it with new soil. Lack of magnesium or phosphorus could cause that.
Are there cultivation near you? It could be contamination by some pesticide or by some fungi like Phyllosticta.