I had a thymoma removed 25 days ago, is it normal to still have a lot of pain and pressure?

Maybe. Recovery after thymoma differs depending on the type of surgery done to remove the thymus e.g. Sternotomy, cervical approach, minimally invasive (vats, or robotic). The pain may take weeks to months to get better. If your pain is not improving or if its getting worse you should contact your surgeon. They can tell you exactly what to expect at your stage of recovery.
Abnormal. But common. Sternal incisions are uncomfortable for a few months. If thoracotomy, may be a bit longer since the ribs are more mobile than a wired sternum. If persists see your surgeon and get an xray.