According to the online conception calculator, you got pregnant from sex between Feb. 22 and Feb. 27th.
If you had sex with the new guy sometime around March 1, that's close enough. If you didn't have sex until March 10 or so, it's hard to tell what's going on.
Thank you, this puts my mind at ease. That calculator really helps. No, any sexual activity with anyone other than my boyfriend was at the end of January