I had sex the day after I ended my last period....

Delayed period :
First of all you have to exclude pregnancy as it's the most common cause for delayed period in your condition . If pregnancy tests were negative your doctor will prescribe medication such as Cidolut nor twice daily for 3 weeks and follow up your condition .
What are the causes of menstrual cycle delay ?

1. Pregnancy
2. Stress amd Anxiety
3. Hormonal disturbance
4. PCO polycystic ovary
5. Thyroid dysfunction
6. Pelvic inflammatory diseases
7. Hypothyroidism
8. High prolactine

What are the sign and symptoms of Pregnancy ?
There are many signs and symptoms which can increase your suspicion of pregnancy , and these include :

• Delayed period .
• Nausea and vomiting .
• Abdominal and low back pain .
• Breast pain .
• Changes in appetite .
• Positive pregnancy tests .

What are the tests used for diagnosis  ?

• Clinical assessment .
• Urine pregnancy test if your period was delayed .
• Blood Hcg level .
• US Abdomen .
• FSH , LH .
• TSH And Prolactine for thyroid disorders and Hyperprolactinemia .