Make an appointment to see your doctor to refer you for imaging of your lower back and hips.
The pain in the leg may be referred pain from the lower spine and hip area. The doctor will also examine your leg.
There may be other reasons for back and stomach pain that can be from the womb, bladder, bowels. As you area also complaining of massive leg pain, I feel that this is highly likely to be connected to the back and stomach pain.
Rest as much as you can and elevate your painful leg. You may find that applying a heat pack to your back and tummy may help to relieve some of the pain. Take pain relief medication as prescribed on the packet. Your doctor may prescribe an anti-inflammatory, but take care with these and only take them with or after food. Sometimes a doctor may also prescribe a stomach medication like Omeprazole to protect the stomach. Anti-inflammatories can make the stomach bleed.
Let me know how you get on.
Best wishes.
Get to the ER and have that checked
request an ultrasound or cat scan of your abdomen also of your back an Mri DON'T TAKE NO FOR AN ANSWER IT IS YOUR BODY. Go to another doc