Zhukov, now a lieutenant-general, is assigned to the First Soviet Mongolian Army Group in July. After being given command of the group he prepares to take on the Japanese. The conflict climaxes at the Battle of Khalkin-Gol, beginning on 20 August.
If you have a normal 28 day cycle, you are most likely to become pregnant when you have unprotected intercourse approximately 2 weeks before you anticipate your period to start.
There is something known as midcycle/ovulatory bleeding, where after the egg follicle burst some (brownish=old) blood spot(s) could be noticed inside your pants, and be mistaken for a slight period. If you had unprotected sex the day before you certainly could have gotten pregnant. The 12 days before menstruation starts you would not get pregnant by having unprotected sex since ovulation is 14 days before and your fertile period is about 120 hours before and 24-48 hours after ovulation. Things are a bit different if your menstrual cycle is very short and your period extended.