Might be pregnant?

Im almost 15 and I might be pregnant I took a test it came out negative but I'm thinking I tested too early. AF is 5-6 days late. I had intercourse 18 days ago. My period is 28 days and lasts for 4 or so days. The end of my last period was July 31st. When should I test or could I be pregnant? I'm really tired, cramps, urinating a lot, breasts are sore and nipples are purple, bloating, morning sickness, slight headaches, weird cravings, and I've had sharp pains in my stomach.