Is this a period or spotting because Im pregnant?

On feb 1st I go my period and it ended on the 6th and the same on march (1st -6th) I was on american baby and went on the chart for fertility which it said I was most fertile on the 12th-16th on both months. On the 16th of march I had sex with my husband that day was one of my most fertile dates without protection. I went on the fertility chart agian and it was saying for april my most fertile date was the 9th-14th. so I assumed my period was going to be on the 28 or 29 of march so I can be most fertile on the 9th of april but it didnt come on that date. So I waited a day or two and it still didnt come. After a week it came on the 5th which wouldnt make me fertile on the 9th I would be most fertile on the 17th If the chart is right about that when I usually have a normal period could I be pregnant and spotting or just really late on my period. I heard if your expecting a period and it doesnt come giving a 7 day period for it still to be a normal period the egg is implanting on the walls of your uterus which causes spotting? Can someone really tell me whats going on? Help