It has no affect on implantation. Yes, it is fine to O during the first few weeks of pregnancy. Some women the further along they get in pregnancy may be advised not to have intercourse but that is a whole other topic. ;)
Organism actually HELPS increase a womens chance of getting pregnant. It will not effect implantation.
I sure hope it's okay! what's the fun in doing the BD TTC if you can't? Hehe...and you can definitely orgasm in pregnancy, my husband and I BD'd the day before my daughter was born; the doctor told us it would help induce labor. I guess it did! but yes, when you do conceive, ask your doctor as you progress about intercourse during pregnancy; orgasm is usually fine the whole 9 months, but actual penetration can be counter-indicated in certain women in the last trimester. :)