This is Dr. David
are you having any fever?
any burning when you pee?
you could be passing a kidney stone causing the back pain
or you could have a slipped disk in your lower back causing the pain.
you might need to see your GP doctor and get stronger medications and evaluation for what is causing your back pain.
nurofen 600mg is pretty strong and doesn't get much stronger over the counter.
make sure you take that with food in your stomach or else it can upset your stomach and over time it can even cause a stomach ulcer.
and make sure you take plenty of water when you take it to flush out your kidneys so you are not dehydrated.
No fever or burning.
that is good no fever
I've taken Ibuprofen a lot in the past (and at high does), so I've been sure to drink a lot of water, and take it with food (or at least milk).