Is it contractions or just sciatica?

Im week 37 + 4. Yesterday i woke up with pressure in my back and it moved to the front as the day went by and came quite irregularly, i timed it to around 45 secs for each cramp and it lasted the whole day and happens usually when I move or when the baby moves then i will cramp up. I can’t tell if it’s because of sciatic nerve pain cause of baby’s position or something more because last night it went away and today, i got no cramps at all and feel tired but that’s about it. Anyone else experience this?