ok .
Right, is the pain is there and not going anywhere else, you're not feeling any pain across your bum cheek towards your hip, or any pain travelling down your thigh anywhere? you'd know if you were.. as i said, its quite sharp pain, and it comes in waves/pulses (i can describe it in more detail as i'm experiencing it very badly right this second.. you can't miss it, its breathtakingly painful.)
If not, i wouldn't have said sciatica.. what it could potentially be is your lumbar spine having some disk issues with them being squished.. that can be caused by inflammation, so painkillers and rest for a week would normally be first port of call, then if it doesn't go, physiotherapy.
If it STILL doesn't go after 6-8 weeks it needs further investigation.
If it is your disks being squished, yes it can flare, it can be positional, it can be aggravated by exercise, bending/lifting, it can be fine for a while then flare up.
My disks around the L5/S1 have gone/dried out, so i am in permanent long term Sciatic pain because the L5/S1 is where the sciatic nerve roots are and mine are constantly pinched/squashed now.
The reason i mention is that if after 6-8 weeks there is no improvement then you have to start pushing for more, disk issues often aren't picked up on x-ray and mine needed a trip through an MRI to detect, despite many many years of pain.