Should I hold off?

Man, ya'll. These past two weeks have sucked lol so here's what's up. My husband and I had unprotected sex on February 19th. The first day of my last period was feb. 13th. (13th-17th) my period is pretty normal. Sometimes it'll be a couple days early or late, nothing major. Well, since the day my period was supposed to come (March 16th) i have taken 4 pregnancy tests. All negative. I haven't been too stressed out or anything. Should I make an appointment for a blood test, or wait a couple more weeks? A friend of mine said to wait, but I really just wanna know. :) thanks ladies! Ya'll have a good night.