Can I make them back into one address again? Because I usually view my wallet balance through blockchain explorer using one address.
Yes. Simply, send coins from those addresses to your "main" address. You can spend coins from specific address by enabling "Addresses" tab in the "View", right-clicking the address and selecting "Spend". You can spend coins from multiple addresses at once. Before right-clicking any address, hold control and use LMB to select those addresses. It might be a better idea to use your Master Public Key to track all of your addresses. You will avoid paying for unnecessary transactions this way.
What is going on?
You need to be more specific. What do you mean by "the ledger showed"? Was it in Electrum or Ledger Live?