weird lump in abdomen

I am 10 weeks pregnant, and I have a lump. Over the last few weeks it has grown, it used to be the size of s golf ball, and I could feel it below my skin on my lower left side.
Now it's about the size of an orange, and you can clearly see it while I am lying down.
It is not visible when I am standing up.
The midwife said it might be my uterus. But when I went to see her that day the lump had disappeared. 
Today it's back and huge!
Has anyone else experienced this and might know if it's normal??
Very scared and anxious about it.