Yes it is OK to breastfeed while pregnant.
Like Rachel said, talk to your doctor.
Also when I found out I was pregnant with my 2nd kid my son was still breastfeeding. Actually he was around the same age as your lil one.
Funny thing is he actually weened himself during the pregnancy.
I was told by my doctor that, while pregnant, the taste & flow of your breast milk changes. All because of the extra hormones you have. So most of the time your breastfeeding lil one will end up not wanting it anymore and will self ween.
It was kinda hard for me at 1st, but You guys will be just fine.
Congrats on the new lil one!!