If you have sex without using contraception, you can conceive (get pregnant) at any time during your menstrual cycle, even during or just after your period.

You can also get pregnant if you have never had a period before, during your first period, or after the first time you have sex.

There’s no “safe” time of the month when you can have sex without contraception and not risk becoming pregnant.

But there are times in your menstrual cycle when you’re at your most fertile, and this is when you’re most likely to conceive.

Understanding your menstrual cycle Your menstrual cycle begins on the first day of your period and continues up to the first day of your next period.

You’re most fertile at the time of ovulation (when an egg is released from your ovaries), which usually occurs 12 to 14 days before your next period starts.

This is the time of the month when you’re most likely to get pregnant.

It’s unlikely that you’ll get pregnant just after your period, although it can happen.

It’s very important to remember that sperm can sometimes survive in the body for up to 7 days after you have sex.

Source
http://www.busygisting.com/2018/06/11/can-i-get-pregnant-just-after-my-period-has-finished/

Yes

What causes menstration??

Lack of secretion of estrogen and progesterone by corpus luteum is what cause menses. The bleeding is caused by lack of implantation on the endometrium of uterus. For successful implantation, the Uterus must be in secretory phase, and the ovulation must have occurred.

Unfertilized ova , will degenerate 2 days after ovulation.

So immediately after menstration , no matured Graafian follicle, and Uterus is not ready for implantation.

No preg, except a ova will be fertilized outside the uterus.