This might sound a bit mean towards your mother, but it's simply my opinion.
Yes, you are her daughter. Yes, you will forever be her "child" even if you are not a child. And yes, no mother wants to think of their child as being taken advantage of or "spoiled".
Having said that, your sex life is none of her business. For her to completely break contact with you over something so natural and beautiful as a consummated intimate relationship is, to put it mildly, petty. Nobody is asking her to like or agree with it, but she needs to understand that it's simply none of her business and certainly nothing to punish you over.
If your biggest crime is having sex with your boyfriend and she saw fit to end contact with you for that, I'm truly sorry. It makes me wonder what else she'll consider a crime in years to come. What if you decide to buy an SUV instead of a hybrid car? Will she punish you for that? What if you get married and have children but don't name one after her? Will she become estranged then? What if you decide to paint your living room orange? Oh, the humanity!
I'm not trying to belittle your situation. On the contrary - I sympathize with you greatly. So much, in fact, that it angers me that your mother would do something like this. You have done nothing wrong, my dear. Your mother may not agree with what you, as a responsible adult, have decided to do with your life and body, and that's okay. She doesn't need to. Family ties should be stronger than that, however. Family should not punish each other with silence for such small things. And even if she doesn't view it as a small thing (and I assume she doesn't), what does she hope this silence will accomplish? Will it give you your virginity back? No. Will it scar you emotionally and possibly sexually? That's much more likely. No child wants to know that a parent would write them off so easily.
I would not pursue this or try to make this right with her. You have done nothing wrong. If she refuses to see that and continues to keep herself removed from your life, maybe that's for the best for now. She needs to understand that you are an adult, your decisions are your own, and that throwing a tantrum will not solve anything. As her child, she should love and support you, even if she does not love everything you do. And giving in to her behavior would be to validate her opinion that, if she becomes loud and stubborn enough, you will give in to her demands, even if her demands are unrealistic. That's not fair to you, and honestly it's not fair to her either. The two of you need to find a middle ground and learn how to be mother and ADULT daughter, not mother and child.