Rachel25-
Hey welcome to the boards! Hopefully you won't be here long.. but everyone is really nice and helpful!
About your problem... have you started af yet? Could you have possibly ovulated later then usual? If your not already tracking your O, I would start. Temping or using the ovulation tests are the way to go. It could be that you ovulated later in your cycle or didn't ovulate at all. There are many different things that could cause your period to be late. Pregnancy obviously could be the reason also. I would wait a week ( I know its hard!) and test again. If you get a BFN again I would go to the doctor for a blood test and to find out the reason your AF is MIA.
Good luck! hopefully you get your BFP! I've been trying for 10 months now and I haven't seen it yet. Keeping my hopes up though! It will happen eventually I just know it! Loads of baby dust to the both of us!!