If you can't even sit, you need to get a stat appointment with your ob/gyn, or go to urgent care or the ER. Even if you weren't pregnant, a lump like that that's not obviously a pimple would be enough to land me at urgent care or the ER, and depending on size, a boil that large might warrant a doctor's visit.
Your right im going to the ER
Please see your gyno asap. This is alarming considering you are pregnant. Blessings - Blu