Hello! I will be assisting you today. It is likely that these two problems are not associated with one another directly. This is the peak of allergy season and in some areas it has been especially bad with all the rain we have had. You likely are having an allergy flare up caused indirectly from an allergic reaction to the tag away active ingredient (The active ingredient is Thuja Occidentalis. Other ingredients include Cedar Leaf Oil, Melaleuca Alternifolia Leaf Oil, Ricinus Communis Seed Oil). The allergic response the the thuja plant has likely caused your body to initiate a strong response to other allergens that are in high numbers this time of year like pollen, etc. After exposure to thuja it can take the body some time to return to a normal allergic response state and flush this substance out of the applied areas. If you are allergic to thuja you are most likely allergic to cedar, juniper, etc. This normally occurs in a couple weeks but may be a bit longer wince you used the product for 3 weeks. The reaction may have been delayed and just shown up recently as the exposure threshold was reached with continued application.
You refer to seasonal allergies having an impact on the Tag Away active ingredient but do not mention/address the possibility of any impact from the lipotropic injection, or its possible effect with the Tag Away content or even the possibility of an allergic response from this. The timing is just so coincidental.
Lipotropic injections with b12 or other fat burning substances (Lipo B, MIC, Lipo Den, etc) would not likely have caused the reaction you describe even though the timing might suggest that it was the cause.