Pain at 18 weeks, should I worry?

I am 18 weeks yesterday and since last night my lower belly/pelvic bone area have been hurting/sore. No other symptoms besides the pain/discomfort. The pain is Even my back a bit. I haven’t gone #2 in 24 hours, but I don’t know if I should be worried or if this is normal. I just am uncomfortable. I’m a first time mom and first pregnancy. I am a nervous person so I don’t want to freak out if I don’t have to...