I hope its normal for it to be painful because I certainly have been having more than my fair share of it lol Mine has taken to stretching out diagonally!! It head bangs my ribs and kicks my hip lol
You really cant judge whether baby is big or not by comparing your bump to someone elses as everyone carries differently. You may be carrying more fluid than your friend or she may be carrying more towards the back, and you the front. If you are worried about babys size then mention it next time you see your midwife, who will measure your bump anyway to keep a check on things. This is your first isnt it? This is my second pregnancy and, although both girls, I have carried differently this time so it really is hard to tell babys size so Im sure theres nothing to worry about.