Hi
I Have this doubts blocking my head.please help me clear my doubts. I get my period on first week of every month. And for August I got it on 4th.then on 26th August I got my period again which I guess should be counted for September's period. And I had intercourse on the 7th day after my period. When can I expext my next period?

If you aren't pregnant, and usually have regular cycles, you can most likely expect your period in the first week of October.

Periods can be off a bit from time to time, however. In answer to your title question, yes, you could become pregnant from sex on the 7th day of your period. If you tend to ovulate a bit earlier than the norm, or just happened to that cycle yourself, with sperm living a number of days, pregnancy can, and does, sometimes occur.

Your September period, if different from your norm, may have just been from an off cycle, but see what happens when you would normally expect your period for October.

ANY time there is penile insertion there is the risk of pregnancy. So yes you can get pregnant from sex on the 7th day of your cycle. Its less likely, but possible.

First having or not having sex, does not effect when you have your next period.

Stress, changes in life, diet can effect the timing (sometimes)

Normally you count the number of days between, and there are a average number,
** not just first week, since, yes, sometimes will may be the last week, of a month, and then first week of the month, for the next cycle.

So, consider, how many days, between.

You become pregnant, if and when you have sex, connected to ovulation, times.
Those can be determined not by online charts, but by proper medical testing