Why does my dog yelp when being picked up?

We got our dog when she was 6 years old, never properly socialized, etc. but she has come a long way and is very sweet. However, my boyfriend can pick this dog up different ways (she doesn't like it but doesn't do anything). If I try to do the SAME EXACT thing she yelps and will bite (she's bitten me once). I am not hurting her at all. The two ways we've picked her up is near butt area and her chest OR her butt area and behind her front legs. But for me, it doesn't really matter, she yelps anyway. She will yelp at other people too where they would just stop and let her go.......Only a couple times have I been able to pick her up. It's very frustrating and not excusable for her to do that even though no one else was bitten. Is there any way to fix this other than simply not picking her up? I highly doubt she was picked up much or at all over 6 years but it doesn't make sense that one person can and everyone else can't. I was wondering what causes this when you haven't done anything different than that one person. I want to work with her to fix issues. Thank you!!