My partner and I participated in vaginal and anal sex. After we were done, I noticed yellow discharge on my underwear. Was this because we participated in anal before vaginal? Is it normal?

It's probably semen.

I hope you were using condoms and used different condoms each time.

If not. You should never do anal first. There is a high risk of infection if you do anal sex first.

So, how long after sex, did you notice the discharge? Was there a odor?