What Causes Delayed Periods With Appetite For Food?

I am a 19 year old healthy female weighting at about 118 at 5'3 1/2 feet tall.I took 5 pregnancy tests last month because i was about 2 weeks late and the first 2 i took(same kkind of test)was faintly positive then 3 more i took(all diffrent kinds of tests) was negitive.i started my normal period may 14th and now am a day late this month.I have been very tired lately and eating weird things(ranch)things i never eat.whats going on?is it anything to worry about?ps.i was so late last month i called the doc to get a test done and then had to cancel it because i started my period.