Lesions, boils, and bug infestations were ordinary and commonplace; nothing supernatural about that, if it happened - if. There is still not even a little evidence of any exodus from Egypt (thousands upon thousands of people would have left traces), so we just can't say that it happened because a fantastic and outrageous supernatural story was told about it and for which there is no other substantial corroboration.
The Bible fulfills its own prophecies because 1) it was edited to show that and was vague enough for it to be easily done (how many hundreds of messiahs were prophesied to do this or that?- lots) , and 2) the people who wrote the new parts read the old parts and made certain parts of it congruent.
The priest who I had as a professor for theology 101 basically put it all down to algae. When two kinds combine from two tributaries of the Nile, the algae turns red, like blood and depletes the water of oxygen which causes the frogs to leave where they perish in the desert sun, which attracts flies and so on and so forth.
There's nothing "supernatural" about God. God created everything that is natural... why wouldn't he use his creation in the way he created it to achieve his means?
The miracle was never "it happened" but "it happened precisely when God said it would happen".
