Isn't it the present tense form? Is to come irregular?
Yes. it is like this for verbs that their root contain only two words like -
רץ, גר, שר
the present and the past are the same
The root contains three letters, but one is dropped to form the male singular past tense, which is irregular. (Yes, I'm a lot of fun at parties, sorry bye)
Is the Hebrew word לבוא also the translation of "to come" in the vulgar sense of this word?