Plan B or implantation bleeding?

Yes. You could be pregnant.

I'm taking it you meant you took emergency contraception on 29th of the month.

He doesn't necessarily have to ejaculate to get you pregnant.

Emergency contraception is not as effective as regular hormonal birth control. It's simply worth a try in an emergency.

If you were ovulating or close to ovulating, then Plan B/Levonorgestrel would not be the best choice of emergency contraception. It works by delaying your ovulation until the sperm leaves your body. Some think Plan B works in other ways, but the Manufacturer does not claim that. They say it's possible, but don't say it does, as it has not been proven.
In that situation I'd have suggested taking the other emergency pill called Ella (Ulipristal Acetate).

If both of you were not tested for sexually transmitted diseases before sexual contact, you may have passed any sexual diseases between you. Some of those can be carried without symptoms for some time, & even by virgins.
If you do end up pregnant, your baby may be exposed to any STD.
I'd suggest getting tested if you haven't already.

You are likely experiencing hormonal symptoms from Plan B, as you can get anything you may experience with a period or pregnancy, or other hormonal change in the body, for example. That doesn't tell you whether or not you are pregnant, though. You can get that but still be pregnant.

Your menstrual cycle could be irregular for weeks or months. Everyone reacts differently.