rained/been raining

There is more than one problem with that sentence. One might write: "It has rained several times in the last two days." One would not write "since two days ago." If you say that it has rained, once or several times, you imply that it is not now raining. If you write that is has been raining, you hold out the possibility that it is now raining. However, then you would also need to alter your sentence: "It has been raining for the last two days." One would never say "it has been raining several times in the last two days." One can either say that it has rained several times, or that it has been raining, in the last two days

I should say that "It has rained several times since two days ago" is not incorrect, it just sounds awkward. I doubt that a native speaker would construct such a locution.

"It has been raining since...." suggests that the rain has been continuous.

"It has rained several times since...." suggests the opposite.

The sentence "It has rained several times in the last two days" seems to say what you want to say.

Thank you both~

But does Set's answer means SINCE XYZ AGO is not English? Is it natural to say this?

-My son John has been a maths major since two years ago.

It is English, it's just awkward, and unlikely to be said by a native speaker. In fact, one hears Europeans using that locution frequently, and i've always suspected that they're just translating their language literally into English. If you use such a locution, you wouldn't necessarily be incorrect, but a native speaker would immediately know that you are not a native speaker.

"My son John has been a math major for two years."

But does Set's answer means SINCE XYZ AGO is not English? Is it natural to say this?

My son, John, has been a maths major since two years ago.

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I only disagree with one of Set's points. I say that it is ungrammatical to use 'since' like that, WB.

for + period

since + starting point

(Practical English Usage - Michael Swan 208 - 2)

My son ... for two years/ since January, 2012

Of course people use "been raining" to emphasize even when the rain hasn't been constant.