Help me!

Hey guys, I’m Chelsea, 21 years old. I’ve been with my partner for 3 years, never used any protection at all, been ttc for 2 year, I’m now on my 2nd missed period, it was due the 1st December then the 2nd of January, I’ve missed both, still keep getting negative pregnancy test, I don’t know what do to, my doctors won’t do anything until I’m on cycle day 21 which I don’t think is ever going to come, I’m really worried incase there is something really wrong with me, any advice would be extremely appreciated.