Excessive night sweats, bad sleep, back pain since 2 weeks. can this be due to my new foam mattress and using two blankets as the room is quite cold?

Probably: Sounds like a reasonable deduction. Try sleeping on a difference surface to see if you feel any better.

Not necessarily: As a mattress change can affect your sleep and cause back pain, but less likely night sweats. Some mattress/sheet combos do not breath well, so I can't say it's impossible that it's all related to the mattress/blanket combo. But I would try to switch over to a lightweight cotton(or other natural) fiber blanket and see how you feel. Otherwise, seek an in-person eval for other issues at hand.