2nd trimester

Hello po, 2nd pregnancy na po ako. Ask ko lang sana if meron dito same as my situation, 2nd trimester na ako week17 pero my belly is too small for 5 months or 17 weeks. I dont feel like I'm a pregnant pero my ultrasound na there's ababy inside.. Medyu nawoworried ako. Sana may maka sagot. T. Y