Painful urination

So I noticed late last afternoon and night a slight burning when I pee, I figured I must be getting a UTI and I'll go to my OBGYN in the morning....this morning I felt fine up until about 5pm it's starting again....I just had a STD test so I know I'm clean, I'm 22 weeks pregnant...I'm a little confused by how inconsistent the burning is being...has anyone else had this issue?