I'm pretty sure I'm not pregnant but wasn't sure what category to put this under.

So I haven't had my period in two months now. Last time I had it was April 18th. I took six at home tests and they all came out negative. I then went to my local church's clinic and the test there came out negative too. Had my doctors appointment last week on Thursday and it came out negative too. Now they want me to come back and I have my appointment on the 12th of July. Im so confused. Its not stress. Nothing has really changed in my day to day activities. This has never happen to me so I'm pretty confused. Oh btw I am 21. Married. Normal weight, pretty healthy lifestyle. Not on any birth control.