Thyroid Problem … ?

I am a 14 year old . I am pretty healthy , except that i have asthma . I went to the doctor just for a check up . I usually have a blood test done every once in a while , so this time my TSH level was high ( not too high though ) . However , the doctor asked me to repeat that test again . Someone from the doctor’s office called and said that all was fine . Then the day after i was astonished by them calling again and saying that in this test it was low !!!! did that test and they were on different days . The first one was in the afternoon , the second one was in the morning ( If times matter !)
I am already seeing the doctor again . I am just concerned it has anything to do with Thyroid cancer.Can it be a normal condition , because my body is still developing ? Please help !