Eh normal je, especially kalau dah 18 weeks pregnant! Your baby dah putting pressure on your bladder, so minum sikit pun terus nak kencing, a few of my mum friends complained about the same thing during their second trimester. The good news is it'll probably get a bit better mid-pregnancy, tapi akan terok lagi masa third trimester, so just accept je this is life now lah! Try minum lebih banyak air time pagi and afternoon, then reduce sikit lepas 7pm so at least dapat tido properly at night.