Why Haven't I Gotten My Period and Experiencing Chest Swelling and Body Pain?

You didn't mention the pregnancy test and also even if it is possitive, you need to see your gynecologist. They can ask for some tests and confirm about pregnancy or any other health conditions
 

Not taking one mini-pill and having unprotected sex may greatly increase the chance of getting pregnant. Within 48 hours is the best time to use emergency contraception. Emergency contraception acts by stopping or delaying ovulation in the body. If you're uncertain about pregnancy, taking emergency contraception would be the best way to lower the chances. 

You might be dealing with some tearing in the labia minora of your vagina. This can happen due to the past activities of masturbation. It is important to look for any color or texture changes. Black color could mean some healing tissue. As long as there is no pain or discharge, it is probably not dangerous. Keeping the area clean and not giving it any more irritation should help the healing.

Pregnancy can occur when ejaculate-containing sperm comes into contact with the vagina. There is still a chance of pregnancy with pre-cum because it may contain sperm. If you find yourself being late on your period it might be one of the symptoms that could indicate pregnancy. In addition to this, you might be stressed out which can also push back your period. Take a pregnancy test just to be safe. 

Pre­gnancy risk is present if sperm e­nters the vagina. Although chances are­ reduced without intercourse­, it remains possible. Signs indicating pregnancy include­ missed periods, nausea, tire­dness, and sore breasts. A pre­gnancy test provides confirmation. Moving forward, condoms offer crucial prote­ction against unintended pregnancie­s and sexually transmitted infections.

It's quite natural for some mild spotting to occur after intercourse, especially towards the end of your cycle. The dark brown spotting you got could be some of the blood from earlier times coming out. It is nothing to worry about, and it sometimes occurs when your body is getting used to the birth control pill. It will probably pass away by itself in a little while. 

Consult a medical specialist near you for a suitable birth control pill considering your allergies. They can recommend alternatives or nonhormonal options like copper IUDs or barrier methods if required.

Pain in the breast while breastfeeding is very common and may be caused by lactation mastitis or milk duct blockage. It is good to see a gynecologist if pain persists, it might be a symptom of a more serious condition. Hence, I advise you to visit a gynecologist or lactation consultant for the right diagnosis and treatment.