Normal pregnancy symptoms: At 3 months of pregnancy, it is common for women to experience headaches and backaches due to hormonal changes, stress, and the body's adjustment to the growing fetus. The absence of pedal edema and normal blood pressure further supports this diagnosis.

Urinary Tract Infection (UTI): Pregnancy increases the risk of UTIs, which can cause backache and headache. Although not as common, it's a plausible explanation, especially if other symptoms like dysuria or frequent urination are present.
Musculoskeletal strain: The growing uterus can cause a shift in posture, leading to musculoskeletal strain, which might result in backache. Headaches could be related to tension or migraine, common in pregnancy due to hormonal fluctuations.

Pre-eclampsia: Although the blood pressure is currently normal, pre-eclampsia can sometimes present with symptoms before the onset of hypertension. It's crucial to monitor blood pressure closely and watch for other signs like proteinuria.
Migraine with aura: While migraines are common, those with aura can have a higher risk of stroke, especially in pregnancy. It's essential to evaluate the nature of the headaches.
Kidney stones: Although less common, kidney stones can cause severe backache and sometimes headache. The pain can be intense and is usually colicky in nature.

Multiple sclerosis: In rare cases, the symptoms of multiple sclerosis can mimic those of pregnancy, including backache and headache. However, this would typically be accompanied by other neurological symptoms.
Spinal epidural hematoma or abscess: Extremely rare, but these conditions can cause backache and headache. They are medical emergencies requiring immediate attention.