amoxicillin isn't known to have an affect on birth control tablets.
and even if they did there was a greater than 7 days period between your stopping them and seeing your boyfriend.
You don't say how long you have been on the pill for, but it can gradually cause your periods to become less heavy or even disappear.
based on the information you have provided I would think it unlikely that you are pregnant, but I wouldn't rule it impossible.
The best thing to do really would be to get a blood test done by your doctor.