These symptoms should resolve in next 3-4 days, if this is an allergy to fish oils, which is definitely the possibility of the diagnosis. If the symptoms persists, after that, you may consider following investigations, if not yet done;
2) Erythrocyte sedimentation rate,
3) Thyroid function tests,
4) Muscle enzymes;
5) Anti-nuclear antibodies (ANA)
6) Adrenal function test
9) Anti-SSA (Ro) or Anti-SSB (La)
10) Coombs test
12) Peripheral blood film / smear.
Hormonal abnormalities like thyroid or adrenal would be looked by the above investigations apart from Epstein virus infection or immune mediated diseases.
Please feel free for your follow up questions.
I would be happy to assist you further, if you need any more information.
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