I had my mirena removed yesterday and I'm discharging a little today and my husband and I had unprotected sex. Could I become pregnant?

Yes, any time you have sex you have the possibility of becoming pregnant.

Once removed, the birth control effect is no longer there, so, as J_9 said, pregnancy will be a possibility.

Even with birth control pregnancy is possible. Without, it's even more possible.

So yes, you could be pregnant. Too soon to tell right now. You'll have to wait and see.

Good luck. :)