Back Pain (Lower Right Side only)

Hey girls, maybe one of you can help me out with this puzzle. I'm am now pregnant with my second child (11 weeks) and maybe three times a day, especially after sitting down or after standing for about 15 min I get this terrible pain that goes away after an hour or so. I'm not sure if it's a musscle anymore. Sometimes it goes away after I have eaten, or after I've had something to drink. Laying down doesn't really help. I'm pretty healthy, thin and work out 1 time a week. 
 
The pain started right after I had my first daughter and started off as a bareable pain that would come and go. After a few years it just got worse and worse and all the doctors would tell me was that is was just a musscle and that I needed to rest. It took about 4 years for the pain to almost go completely away, but even so I could still feel it from time to time. 
Now that I'm pregnant again, it's back... Every day..
Is this a common thing during pregnancies?
I'd like know what you think..and what your experiences are with this. I've read a ton of articles already..