How do I know whether he had sex up my bum or actually in my vagina?

Well, how do you know that he didn't try to put his penis in your nose or your ear? You can feel the difference between your nose and your ear. Likewise, you can feel the difference between your vagina and your anus.

When you defecate, can you feel your anus then? Can you feel where it's located on your body without touching or looking at it? If you are not disabled, then I would be very surprised if you genuinely did not have some kind of spatial anatomical awareness.

Assuming that you genuinely cannot feel the difference between your anus and your vagina, you can learn that difference. You'll need some latex gloves or some finger cots (they're like condoms for your fingers). You can also get a hand mirror, but it's not necessary. Put on a glove or apply finger cots to your index and middle fingers. You can hold the mirror with your other hand to get a view of your anatomy. Using the covered fingers, touch your vagina. Get a good idea of where that sensation is coming from on your body. Memorize where that sensation is coming from. If you're comfortable with it, you can insert a finger into your vagina just as you would if you were applying a tampon. When you're sure you know where your vagina is, then you can move on to your anus. Touch your anus gently. Insertion is not necessary. Get an idea of where the sensation is and learn where your anus is without looking at it.

If you really have to try this, do NOT touch your anus first. Touching the anus and then touching the vagina can transplant fecal bacteria from your anus into your vagina, which will cause a bad infection.

When you're done, discard the cots and gloves and wash your hand with hot, soapy water.

And for more info, please read:

• Pink Parts - Female Sexual Anatomy

• Anal Sex: Any Difference?