Brief Answer:
Read below.

Detailed Answer:
I read your question carefully and I understand your concern.

There can be several causes to morning headaches. Both lack of sleep and oversleeping may be related to morning headaches. Withdrawal from caffeine may also be a cause.

In case such triggers are not present then chronic tension type headache may be considered, often in the setting of depression, but usually there is a history of episodic headaches before. Usually without nausea but sometimes may be accompanied by it.

Neck arthritis may also be a cause of headache involving the neck and the back of the head. Nausea and dizziness may be a feature as well. However unless you are known to suffer from a rheumatological condition or have a history of neck trauma I would say it is unlikely at your age.

The issue of allergies may indicate another possibility which is sinusitis commonly associated with allergies. If you also have issues of a stuffed, runny nose it would be the most probable cause.

If though at the end of the day none of the above mentioned factors are present, then if you are someone without a previous history of headaches, manifesting a new daily headache with nausea, I would schedule a neurological visit and head imaging to exclude brain lesions (which shouldn't be a cause for panic as it is unlikely at your age).

I remain at your disposal for other questions.

---