Your father is required to account to the court for the money and to close out the estate and distribute to you when you turn 18. If he fails to do so, he can get in big trouble. I would petition the court, if he refuses to comply. I know it grinds you to need to use some of your money to pay an attorney, but it makes sense for you to at least consult an attorney, here. The attorney will know the procedure for petitioning the court, as well as the form and format to use. The attorney may also know how to seek sanctions from your father, for forcing you to take this to court.
Best of luck to you! Hopefully, your father will decide to back down, before this becomes a court situation.
*** LEGAL DISCLAIMER I am licensed to practice law in the State of Michigan and have offices in Wayne and Ingham Counties. My practice is focused in the areas of estate planning and probate administration. I am ethically required to state that the above answer does not create an attorney/client relationship. These responses should be considered general legal education and are intended to provide general information about the question asked. Frequently, the question does not include important facts that, if known, could significantly change the answer. Information provided on this site should not be used as a substitute for competent legal advice from a licensed attorney that practices in your state. The law changes frequently and varies from state to state. If I refer to your state's laws, you should not rely on what I say; I just did a quick Internet search and found something that looked relevant that I hoped you would find helpful. You should verify and confirm any information provided with an attorney licensed in your state.
You should be able to find a lawyer willing to represent you and who may wait until the funds are recovered to receive payment. It is also possible that your father will be ordered to pay your attorney's fees and costs incurred out of his own funds if he is found to have wrongfully taken or withheld your funds. Are both you and your father residents of Maryland? Your reference to being an adult in "my state" suggests you are not both located here. Where is your father located?
It would be essential to see the guardianship papers and read the face sheet of the life insurance policy, but it would seem likely based on your recitation that your father was acting as a fiduciary for funds belonging to you, and there are no facts presented that he, in fact, used the funds for your support or reasonable needs within whatever guidelines were applicable. If that turns out to be correct, it seems plausible that your father may have violated his fiduciary duties by seizing funds as trustee. That is a cause of action, and there are many ways to approach it, some of which involve relatively little legal effort. It depends on the factual and procedural setting. Now that you are 18, it is imperative that you contact a qualified lawyer and enforce your rights immediately. Failure to enforce may be deemed a consent to your father's use of your money. This Avvo system seems to claim lawyers can call you after posting responses. I disagree. Calls with you that you did not initiate are unethical solicitations. You may feel free to call me in Rockville at 202-530-0100 if you want to schedule an appointment.
I am sorry for your loss and the difficulty you are having with your father. I do think the best approach would be to retain an attorney but I see in your post that you cannot afford one. You may be able to get some guidance from the Guardianship Court that is overseeing your case. If he is the court appointed guardian he has to file accountings with the Court. You may also want to Google pro bono services in your State. There may be a group that will work on your case for free. It never hurts to look. Good luck.