28 days late and negative home test

So I am 28 days late now. I'm getting super frustrated now because I have taken 4 home test and they all are negative. We have been TTC for about 8 months now. I don't know what could be wrong. I haven't been under more stress than usual. I have had some symptoms but they come and go. I also don't know if they are just in my head or real. I just really am getting tired of see one line.