2007 Prius - Red Triangle, Overheating sign, Coolant disappearing

I've searched across the forum for clues to what might be the issue, but would like to troubleshoot a bit more and get to know possible fixes.

Car: 2007 Prius
Mileage: 95k miles

Issues began happening days after driving over 8 hours with a fairly heavy load (moving home), our Prius got the red triangle and then moments later a red thermometer sign while going slightly uphill. No issues during the long drive.

Since then, I have experienced the following:

• ICE coolant reservoir was empty and I had refilled reservoir (twice) with pink coolant
• Weak acceleration on flat roads and weaker on hills
• Heater not working
• Red triangle/overheating symbol whenever driving longer distances + uphill

My initial thought was gas bubbles in the coolant system but would that explain the missing coolant? After some more research, is it possible it is a head gasket issue? How do I diagnose/fix this issue? How much would a mechanic charge for this?