Hi there, thanks for your question at HCM
Most commonly Low back ache can be attributed to bad posture or muscle pull/ strain due to abnormal
stress on back like sudden twisting movements or lifting weights etc. But I think it needs further work up since. 1. you have
back pain for after sitting for 20 minutes( not expected at your age). 2. you have start up pain( pain on getting up form sitting position- indicates some form of instability in the back , muscular or bone)3. new onset pain like sensation in one of your legs( might suggest pinching of nerves in back) 4. no significant improvement in pain after several treatments, heat and medicine( suggests severity of underlying etiology) and 5. you have relief of pain on bending forwards( can suggest
arthritis of facet joints - joints in your back). The most basic work up will include a thorough physical exam and
X Ray of your spine. Further course of action will be decided based on them. Online solutions might help you in muscular strains and postural pain , but not if there is some pathology in your back.The lump like feeling in your back can be due to muscle spasm or bony instability, which further calls for a visit to your physician to be more sure.
In the mean time,I would suggest you to go through websites on ergonomics. Ergonomics is branch of science which deals with posture adjustments according your livelihood. It will help you choose a posture most suited for your daily routine. Also core stabilisation and back strengthening exercises wil help support your back in the long run.
Hope this helps.
All the best. Regards.
Dr.SBK