B.Sc

Yes, you can. IGNOU offers credit transfer. Credit transfer means allowing a student at another university to get enrolled in IGNOU for completing an equivalent degree on the basis of credit transfer obtained by him from that university. A student thus not appeared in the exam of that course which are found equivalent to and for which appropriate credit would be deemed to have been acquired for purpose for fulfilling the IGNOU requirements for award of a degree. Of course, there are some rules. You can check it in the prospectus/programme guide of IGNOU. And yes, you can do both at time one with regular duration and another by Certificate programme. But in my view don't do that, it will be too tough for you.