Upset about what has happened to my 40 yard dash

[tengel21]

I am a junior in high school 193 6'3 17 years old. I have been enrolled in strength and cond class since August I ran 4.7s 4.6s and a high 4.5 here and there. I ran these times consistently through out the semester then we were off for Xmas break for two weeks I came back and got timed at a 4.9 first day back then I started running 4.9s these past 2 weeks. Anybody know what the problem is? I am getting very down on this problem