Shell - I can totally sympathise. I had this problem from around 30 weeks with ds1 and have got it again now. The pain in my shoulders spreads down to my upper arms a bit too. My physio first time around told me to wear bras with really wide, supportive straps which do help a bit although they're very ugly! I think it's just the strain of a big, heavy belly and probably heavier bbs too all pulling down on your shoulders. Panadol can help but you probably don't want to have that too often (I used to just have 2 before bed time) and get as many massages as you can! Maybe a warm bath too?