When should I take a pregnancy test?

Courtney
TL;DR Not sure if physically stressed or pregnant. 
Hey guys, I'm in a strange situation. I forgot to take my BC for about a week around July 20-28 or so. My bf and I had sex in that time without a backup method. My last period started July 10 and I haven't had one since then, and my cycle is normally only around 28-30 days long. Around August 4-8, I felt some cramping but no bleeding or spotting with it.
Here's where things get interesting: My bf and I haven't seen each other since July 28, because I've been out in the field for military training. Training has delayed my cycle in the past, but never more than a week.
Should I chalk up my irregularity to the extra strain my body has been under the last few weeks? How much longer should I wait before I start becoming seriously concerned about the possibility of being pregnant? I did take a test today that was negative, but I also took it in the middle of the day which I know isn't recommended.
Any help would be appreciated. Thanks!

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