AWS Lambda different IP address for each Lambda

I am wondering if it's possible that our because our volume is low we just always end up using the same container hence the same IP address?

Yes, that is exactly the reason. A container is only spawned if no containers are already available. After a few minutes of no further demand, excess/unneeded containers are destroyed.

If so is there any way to prevent this?

No, this behavior is by design.

When you redeploy the lambda it seems to use a new container. So you can automate this deploy process using awscli to get a new ip on command.