Brief Answer:
No indication of a serious brain condition.

Detailed Answer:
I read your question carefully and I am sorry about the symptoms that you are experiencing.

I do not believe that you have any serious life threatening cause such as the ones you mention though.
An aneurysm in itself does not cause such headache. As long as it doesn't rupture it usually causes no symptoms, if it ruptures it would be a very sudden, abrupt, very intense headache, often accompanied by other neurological deficits and alteration of consciousness, so certainly not a ruptures aneurysm. There are some rare cases when big aneurysms cause symptoms without rupturing due to compression of surrounding structures, but they are very rare cases in general and not this type of headache you describe. So I definitely do not think you have an aneurysm as a cause for your headache.
As for a tumor, while technically I can't rule it out without examining you for other neurological deficits, I still do not find your headaches to be indicative of that. It doesn't have the tightness in the neck and back you describe, overnight it usually worsens being worse in the morning and also has other neurological deficits most of the times. It usually would be progressively worsening with vomiting episodes, little influenced by Ibuprofen.
Your description seems most probably in the setting of tension type headache. It is the most common type of primary headache (primary meaning no identifiable cause) and is often triggered or exacerbated by stress and anxiety. It is usually alleviated with Ibuprofen. Relaxation exercises are a good preventive means, when still very frequent daily preventive treatment with amitriptyline is beneficial.
Another cause which can be considered might be sinusitis, but usually that is accompanied with nasal congestion and discharge, pain on local pressure on the sinuses.
Anyway it is good you are being seen by your PCP in order to check for neurological or sinusitis signs, as well as for signs of other conditions like anemia, high blood pressure which can at times be a cause of headaches.

I hope to have been of help.

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Brief Answer:
Read below

Detailed Answer:
Yes it is true that it is commonly one sided, but there are many cases it predominates on one side.
If it is persistent though and never switching side, without a local cause such as sinusitis, then you should discuss with your doctor the possibility of brain imaging. If he doesn't find any additional signs in his exam though I am positive that the test would come back normal.

I hope you will get better soon.

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