You have three years from the date of the retaliation to file a claim. There can be multiple instances of retaliation leading up to your termination, so you will want to file before the statute of limitations has run on the first claim.
Generally, if you are within the statute of limitations, you can include this claim with your qui tam case. Nothing will happen while the government investigates the fraud, but once the case becomes unsealed, you can litigate or settle these claims together.
Bracker & Marcus LLC routinely litigates retaliation claims in conjunction with qui tam allegations.