How long it takes for a strain to heal depends upon how much damage was done at the time of injury. Strains are graded from I - mild, no structural damage to IV - complete rupture of the muscles/tendon. So, the larger the damage the longer it takes to heal. It can take up to a year for severe injuries.
Also, you have to give it an opportunity to heal. Which means some rest and then physical therapy. Hope you get better soon. Good luck.