when should my period be due? getting a bit concerned!!

i have a 6month old and been on the pill since he was 3wks old. all was going great until last month when i had to go onto antibiotics and was told they could mess with my pill.... i had around 1week off pills left when i started taking my tablets and i came on my period 2 days after starting the antibiotics! so stopped taking my pill when my period started eventhough i had 5 pills left. it was a normal 5day period.... so i came on a few days before halloween, so around 29th october. before having a baby i always had 26day cycles... so i somewhat assume although could be far wrong, that i would go straight back to having 26day cycles?? so if thats the case im somewhat late.... when should my period be due? i keep getting cramps like its starting... but then it doesnt