If my boyfriend usually pinches his penis to get rid of the pre cum and resume like 5 minutes later the days of my uvulation, could i become pregnant?

Yes: The pre ejaculate fluid can contain sperm and does not stop at at set time before ejaculation. It also can contain the HIV virus if your partner is infected. I recommend using a more reliable birth control method and consider barrier methods such as condoms if you have multiple partners or are concerned with sexually trasnmitted diseases.

Yes: Most definite yes. It doesn't stop that way stream down entire urethra.

Yes: Any fluid from the prostate can possibly contain sperm. Barrier contraceptives such as condoms or female contraceptives should be used.