Hi Welcome to HEALTHCARE MAGIC..
I have gone through your query and can understand your concern...
Yes unprotected sex can lead to
pregnancy. However chances of that depends upon many factors such as
1 Whether you had sex near to ovulation dates or not. There are increased chances of pregnancy when you have sex near ovulation dates.
2
sperm count & motility of your boyfriend
3 whether your implant is releasing some hormone or not
Therefore you might be pregnant. Your symptoms like feeling nausea,
tiredness, mood swings, back ache, sore breasts, frequent urge to urination &
abdominal bloating could be pregnancy symptoms. Pregnancy cause
hormonal change leading to these symptoms
You are advised to do a pregnancy test
Hope this information helps