I would suggest you could be having some muscle separation. I had it and I remember it burning like that and it was so bad at times I couldn't even sleep. The midwife sent me to the physio and I told her and she said that the pain I got was that so I would be checking into it just in case. If it is there are measures you can take during your pregnancy to help to minimise it as you will need physio after if it's bad like mine is.