Mine are so subtle that I wouldn't notice them if I don't happen to have my hands on my belly to feel it hardening. TMI: after you orgasm, your uterus will feel hard and contracted because it's the same hormone (oxytocin) involved. This is why pelvic rest is recommended for women with "irritable uterus". So, use that as your baseline. Not to be creepy by recommending this, but next time, right after ... feel your tummy. It'll be very firm all over, and you can't press through it like you normally can. That's a contraction. It doesn't need to hurt. (For this purpose, it doesn't count if you didn't come).
I sometimes notice it right when I wake up in the morning, scampering down the hall to pee. My belly gets very very firm, but that's about it. It lasts a few minutes and then disappears.