Right --not only would there have been the problem with the age…but the force too can thus invalidate things even if they were of age.
Yes it would be fornication if one has entered an invalid marriage.
Yikes!

No! This is not correct!
Canon 1060 assures us that “(m)arriage possesses the favor of the law; therefore, in a case of doubt, the validity of a marriage must be upheld until the contrary is proven.” That is, unless and until the marriage is
proven invalid, then it is presumed to be valid! (Therefore, no fornication!)
Let’s look at the OP’s question, though…
Let’s say that before you reached the age of consent,
I’m not sure about “age of consent”, but c.1083 lays down the minimum age for valid marriage: 16 for men, 14 for women. Are you saying that the marriage happened when one or both spouses were younger than the requirements, and without a dispensation for age?
you were forced to marry someone for political reasons
you mean that there was a defect of consent?
Here’s the kicker. You’re saying that there was at least an undispensed impediment and a defect of consent, and yet the marriage was witnessed in a Catholic Church? Wow.
Nonetheless, “favor of the law”, remember? Presumed valid.
You also later realize that your marriage is without question, invalid
No: your marriage is valid. Until you went the nullity route, or the convalidation route, your marriage is presumed valid. (You could nuance your statement by saying that, “you later realize that, if you attempted the nullity process, your marriage would be found invalid”… but that’s a whole different statement!)
Wrong. You ARE married. (Congratulations!) Now, the question is, what do you want to do? If you wished to stay married (as you seem to be saying), then you would approach your pastor and ask about convalidating your marriage, which would include in it a new manifestation of valid consent (since there seems to have been defective consent earlier). Moreover, presuming that the husband is now at least 16 AND the wife is now at least 14, there is no need to worry about the impediment – it no longer exists (at the time of the new consent).
At the point the convalidation happened, the (first attempt at marriage) would have had the presumption of validity, and the convalidation establishes the validity of the marriage from that point forward.
Would it be fornication to continue to have marital relations with your significant other?
No.
Are you morally compelled to seek to be properly married first?
Interesting question – is there a canon lawyer in the house? My gut feel is “no”, since you already
are married; but if it sets your mind at ease, then convalidation is a wonderful way to approach the issue!