I was replying to your post in the duplicate thread about your nosebleeds and headaches but the thread has gone. Luckily I didn't lose my post so will copy and paste it here...
It will likely be the fish oil. Loads of supplements thin the blood and fish oil has caused me issues as well. Often guys will be using various supps that can have a contributing effect and they don't realize it. Examples of supplements that thin the blood include turmeric, vitamin e, ginger, fenugreek, zinc and garlic etc. If I ever start a high dose of fish oil I am pretty much guaranteed to get a nose bleed within a few days. Although you are using a few things that should have the opposite effect.
Regarding the headaches it's impossible to know without more details. It could be a simple pick and it's just the fish oil but it's hard to tell because obviously headaches could be caused by 1001 things. Generally fish oil is known to help (very well) with headaches but some people have reported it causing them. I know you are using a multi vitamin but a vitamin deficiency is a common cause of headaches. Too much homocysteine is a very common cause of headaches and b-vitamins lower homocysteine levels. Vitamin B2 is especially important when it comes to headache prevention. Too many fat soluble vitamins can also cause headaches.
It's hard to say because often too much or too little of something could be the cause of the same issue (vitamin d and headaches being an example). If you could get comprehensive bloodwork (including vitamins and minerals) that would definitely tell you a lot. I include minerals because another cause of headaches is not enough sodium so that is something to keep an eye on. Many drink loads of water but don't add the necessary sodium to go with that fluid intake and that can cause numerous issues. I am rambling on but just trying to help by going over various things because one of them might ring a bell in a sense and could help.