late AF(please help!)

My period was supposed to come Friday or Thursday and I haven't gotten it yet. I've taken 2 pregnancy tests (one Wednesday and one Saturday) and they are both negative. However, I've experienced extreme fatigue, sensitive breasts, nausea, and mild cramping. I never get those before my period starts. It doesn't seem like my period will be starting anytime soon. My cycles are usually 28-30 days long and it's now day 34. How late do I have to be in order to be seen by a doctor?