I've experienced BH since 16w (you start getting them earlier than that, but most people just don't notice) and feeling them early is definitely not an indicator of anything wrong, however if they're as regular as you describe (every 5 minutes for a prolonged period) and they don't ease off when you change what you're doing (if you're sitting, walk around a bit. if you're being active, rest a bit), I'd be concerned. Especially as you've had cerclage your pregnancy is already seen as higher risk in terms of pre-term labour I'm guessing? I'd definitely get it checked out, preferably at the ante-natal ward rather than the GP as they'll have specialist knowledge.
Do you still have them when you change position or lie down? If so, I would go and get checked out. It's almost certainly nothing but as you've had a cerclage and are bound to be very anxious about this I would go and get checked out.