It sounds to me like you didn't ovulate this month. When a woman doesn't ovulate, her ovaries
may continue to be stimulated by the pituitary, which can cause high estrogen
levels (after ovulation
, estrogen drops). The high estrogen can cause breast soreness and nausea
and other symptoms of pregnancy.
When a woman doesn't ovulate, she can also experience spotting
, since the lining has built up and can bleed a little.
Not ovulating is common, often due to stress but sometimes from other things. It usually takes care of itself over time. If you wish to become pregnant, then you might wish to see your doctor for evaluation.
If your next period is late, that won't be surprising, since ovulation is what causes the next period to come 14 days later.
Symptoms that are due to pregnancy don't usually start until around the time of the missed period. Best wishes.