Everyone has health problems, but this is not a reason to give up the joys of sex.
Runny nose
We want to surprise you. If you have a stuffy nose, sex is literally prescribed for you. During arousal, the sympathetic nervous system causes the blood vessels in the soft tissues of your nose to constrict. Less blood pressure in the nose - less inflammation, your nose opens - and here it is, relief.
What poses to choose? The ones where you won't lie on your back. But try everything to understand which one is less difficult for you to breathe in.
Start with the spoon pose. It is quite comfortable, soft, and in it you will not sniff your partner's face.
My knees hurt
Knees can hurt for a hundred different reasons, it's not our goal to sort them all out. What to do? Try having your partner sit on a chair and sit on top of it with your feet flat on the floor (not tiptoe like in the picture).
The missionary position can also work.
The lotus position is also a good option for people with sore knees, as long as you don't experience pain when bending them.
Back hurts
Only a toothache can be compared with back pain, and if you are its victim, we sincerely sympathize with you. Let's figure out how to help your trouble so that involuntary celibacy is not added to your back pain.
If you're trying to have sex in the missionary position and it hurts, put a pillow under your back.
And here is another position that can help: face to face, very gently, carefully and without sudden movements.
It will be better if you have sex on a hard non-spring mattress.