Could i be pregnant?

3 weeks ago I had unprotected sex with my boyfriend and he came in me. As of today I've began to feel super nauseous and noticed my boobs are tender. My period is almost a week late, (according to glow). glow has been decently accurate for me on predicting my monthly visitor. I don't have the money to get a test until Friday, and am fishing for other opinions. I am already a mother to a 20mo old little boy and when I found out I was pregnant with him it was 3 weeks after conception and I got sick with flu like symptoms for a good week. So far none of that, just being nauseous.