OMG this is exactly how i've been feeling, i'm actually quite upset about it coz it really really hurts to stand up, its more to do with movement of my legs, it gets sore to stand up and start moving. Its just normal pelvic pain, I had it very bad with my first, and even though its more common to get it in later pregnancy alot of ppl get it early on too.
Unfortunately there's not much that will take it away. But I found with both pregnancies that it gets worse the day after i've done lots of walking, especially if i've been walking fast the previous day, so it really is better to take it easy. I've been walking very slowly the last cpl of days (i do alot of walking each day).
Oh and sometimes I go days without it and days with it. Its due to ligaments being loose ect, but towards the end of pregnancy it does get pretty sore with the added pressure of baby on pelvis.