Thank you for your question to HCM.
Pain and inability to lift the arm sideways beyond a particular point but easily able to lift it towards front indicates joint stiffness
one of the reasons being frozen shoulder
. Subacromial bursitis
will also be painful on sideways movement and a tender spot can be elicited on the side of point of shoulder. An examination by physician can differentiate this.Muscle weakness
if at all is the cause will never give painful restriction of movement though weakness of longer duration in the absence of physical therapy
can lead to joint stiffness.
Regarding your current symptoms treatment would be
1 Analgesics like ibuprofen or naproxen which are antiinflammatory as well.
2 Physical therapy to improve range of motion of the joint.
3 Local injections can help with pain relief.
Hope this was helpful. I would be happy to answer any questions you may have.