I am 24 weeks pregnant. I quit smoking 6 weeks ago, and had a cold 4 weeks ago. I noticed a pain in my armpit and went to rubb it to see if it was an ingrown hair, but there was no ingrown hair, but instaed a marble sized lump deep under my skin. And it was tender to the touch. Is it just a swallen lympth node or something else? Do I need to go see my Doctor?

Yup you do... off to the doctor you go! Could be a swollen Lymph node or it could be a cyst or it could be a boil... I can't diagnose anything over the internet and neither can anyone else, something like this you need to be seen in person by a qualified doctor. You being pregnant you really need to be health concerned as you are looking after two people and one of them can't just hop off to the doc by him/herself!

Yes! Get to the Doctor! No one knows your body better than you do, but when you are uncertain about a lump under your arm, whether it hurts or not, get it checked. Especially having a baby in the belly, you don't want some sort of infection starting and going throughout your body. Its better to be safe than sorry! Don't wait, go... NOW! :D Good luck