Why Do I Bleed During Sex Sometimes?

It is not "normal" to bleed during intercourse, but it is not that unusual.
Possible causes are
1. The sex is a bit rough
2. There could be an erosion on the cervix
3. There is a polyp in the womb near to the cervix

If 1. Does not apply then a medical opinion should be sought, as 2 & 3 require investigation.

Sometimes I bleed after having sex but not all the time.need an answer.what should I do I use protection

Contrary to your mans ego, your frame is equipped to deliver a baby, therefore your man's penis is in no way too large for your body to handle. (sorry BF) If your sexual incounters are on the rough side of things he could be tearing the fragile walls of your vagina through friction not size. Use more lubrication to ease the friction and that should work for you.
If that doesn't work, see your GYN for more suggestions.

i had a partial hysterectomy but i still bleed after sex with my husband why is that

It is possible that you have erosion on the cervix, or a uterine polyp that sometimes protrudes through the cervix. For either of those see a Gynaecologist.

Ive had a baby 3 months ago and when I have sex with my partner I start to bleed afterwards is this normal
?