You could well be pregnant but you'll just have to play the waiting game, sorry! Try another test tomorrow with FMU (first morning urine). There isn't much point going to the doctor yet as they won't generally do a blood test until you've received a positive pregnancy test. However, if you're still getting negative tests and your period is late by a week or more, it could be worth a trip to the doctor. Pregnancy tests are pretty reliable these days though so they should detect a positive pregnancy. Keep trying, try some different brands too! I highly recommend the digital tests too as they are super sensitive but they are a bit pricey.

If your cycle is pretty standard, then you are *likely* to ovulate around the middle of your cycle but it does vary for everyone. Sperm can survive for up to 5 days though so even if you o'd late, you could have caught the egg with either of your BD sessions.

The tender breasts are a good sign although I didn't have breast tenderness until about 7 weeks. In saying that though, pregnany symptoms are different for everyone. Most of my symptoms didn't kick in properly until 6 weeks then I really knew all about it, LOL!

The chances of twins is a hard one to determine. Fraternal twins are heredity but generally on the woman's side (see info below):

Factors that increase the odds of having twins
Some women are more likely than others to give birth to twins. The factors that increase the odds include:

Advancing age of the mother – women in their 30s and 40s have higher levels of the sex hormone oestrogen than younger women, which means their ovaries are stimulated to produce more than one egg at a time.
Number of previous pregnancies – the greater the number of pregnancies a woman has already had, the higher her odds of conceiving twins.
Heredity – a woman is more likely to conceive fraternal twins if she is a fraternal twin, has already had fraternal twins, or has siblings who are fraternal twins.
Race – Black African women have the highest incidence of twins, while Asian women have the lowest.
Assisted reproductive techniques – many procedures rely on stimulating the ovaries with fertility drugs to produce eggs and, often, several eggs are released per ovulation.

I hope that helps a little. Good luck and fingers crossed you get your BFP very soon!