Hi and welcome to HCM!
Thanks for posting your query here.
If you got the period there are less chances of getting pregnant. Chances of getting pregnant will depend on the ovulation time or the fertile period. In a normal 28-30day cycle the ovulation day will be on the 14-16th day. Hence a period from 10 to 18 day from the start of menstrual bleeding is considered as fertile period. As you are not in that period chances of getting pregnant are very less.
Feeling tired and breasts looking big could be your psychological feelings. Hence you dont worry. If still you have a doubt a urine test can rule out the pregnancy
Hope this is helpful to you.