Doeesn't sound like the junction-box wiring scheme, so likely to be loop-in scheme, but your description of two terminals each with three wires doesn't sound right, unless one is a short wire linking terminals within the rose?
What would be normal ...
One of the terminals with three wires (red?) are the permanent lives, one in from the upstream rose, one out to the downstream rose, and one to the switch.
The neutral terminal should have two (black?) wires, one in from from the upstream rose, one out to the downstream rose, and also a (blue?) wire going to the bulb (possibly a link to the underneath terminal?)
The other wire (black with red sleeve?) coming back from the switch should go to the bulb (or possibly another link to the other underneath terminal?)
Depending on age, you may also have an earth terminal (green/yellow?) with connections from downstream, to upstream an to the switch.
Though if you're not looking at a rose in-between two other roses, or if you have some unusual two/three way switching it might not be as described. Also that would be the UK norm, not sure of Irish differences.
A photo would probably clarify ... but not directly solve your problem.