What you are doing right now is called dollar cost averaging, which has proven to be quite effective, though it will not beat jumping in with a lump sum at the beginning.

Since you don't have the lump sum to throw into BTC, my suggestion would be to stick to your schedule; the mental stress you accumulate by worrying about what the future price might be is not worth the result.

There's no guarantee that the price will go down in 2-3 days. In the first approximation, it is just likely for BTC to be higher in 2-3 days as it is likely to be lower.