It is difficult to diagnose without performing physical examination. On the other hand, the lower abdominal pain and back pain are frequently the early symptoms of pregnancy. As you have had a missed pregnancy once, it is advisable that you make an appointment with your gynecologist for an evaluation. A test can be taken between 1 and 2 weeks after a missed period.

It's important to know why periods can be missed. Stress, sudden weight change, intense workouts, hormone irregularities, or some diseases might lead to this. It may not be safe to take period pills without knowing what caused it. Instead, go back to the doctor. They could conduct tests and find out the exact problem then give appropriate treatment.

It is common to worry when your first sexual intercourse is not on time. It may be a bit late due to stress, weight gain hormonal imbalance, etc. If you think that you might be pregnant then do a pregnancy test to calm down yourself. Remember that every time one should use a condom during sex to avoid pregnancy and getting infections like HIV. 

I'm really sorry to hear that you've been dealing with this problem for so long. Chronic yeast infections can become a very big hassle and might warrant your doctor finding a new strategy. It's very important that you go to a doctor who can look at what's going on with your particular case and who can prescribe treatment to address the problem head-on because antibiotic use is one of the main causes that brings back the infection. Products like over-the-counter antifungal might alleviate the condition, but the advice from a healthcare professional is equally important. It’s also necessary for your partner to seek medical help and the doctor might prescribe other drugs for the next vaginal treatment. By working together you can come up with surefire tactics to facilitate and prevent future symptoms. Always remember your well-being and comfort are important so, make sure to get help from a professional.