Is it safe to have sex 7 days post d&c/polypectomy/hysteroscopy if there has been no bleeding? or will the chance of infection be too high?

Probably safe, but: I usually recommend 2 weeks, but I think it's not always necessary. Most people heal faster than that, and we are just being very cautious. I like to examine my patients prior to resuming intercourse. Also, you may be a bit tender on the inside, even if you feel fine on the outside. If you can't wait, and you want to be as safe as possible, you could use a condom.