Input tax credit of purchases

Yes.

Input tax credit which was not reported may be availed while filing return for subsequent month(s). Further, GSTR-3B does not contain column for reporting of previous month figures. So, should be reported on net basis in the next return.

As per Circular No. 26/2017-GST, dated 29.12.2017

yes yes yes u can claim 

Missed out ITC can be claimed in next GSTR3B returns.
ITC can be claimed only within one year from the date of issue of tax invoice relating to supply. In any other case, the last date to claim ITC is earlier of the two below:

Before the filing of valid return for the month of September following the end of FY to which such invoice is related, or Before the filing of the annual return

Note: As per section 44, the last date for filing of annual return is 31st December following the end of the financial year.