The left-sided curvature that has developed over 6-7 years with slight discomfort on erection is commonly seen in Peyronie's disease, where a fibrous plaque develops inside.
Masturbation does not directly cause a permanent bend in most cases, but repeated friction / micro-injury can be a contributing factor for plaque formation.
The discomfort and reduced firmness you are feeling should be evaluated.
In Homoeopathy, medicines like Thiosinaminum, Silicea, Calcarea fluorica, Graphites etc. are often considered for such complaints, but the selection depends on exact degree of curvature, duration, pain, and your complete case history.
Next Steps
It is not advisable to self-medicate for this. I would suggest you get one physical examination done by a Urologist / Surgeon to assess the plaque, after that Homoeopathy can be planned as supportive treatment.
You can consult me online with detailed history for proper guidance.
Regards,
Dr. Madhavi
Homoeopath