My doctor kept my levo dose the same when I started Cytomel.
Cytomel got my FreeT3 level to where I needed it to be but, my FreeT4 level dropped in the process (this is not uncommon - it's a biochemical thing). It took 4 levo dose increases to restore my FreeT4 level.
You do not have subclinical hyperthyroidism when you are taking thyroid hormone replacement meds and have a below-range TSH.....if anything, you are optimally medicated.
Per the last sentence of this 2003 article published by the National Institute of Health:
http://www.ncbi.nlm.nih.gov/pubmed/12915350?ordinalpos=1&itool=EntrezSystem 2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pub med_SingleItemSupl.Pubmed_Discovery_RA&l inkpos=4&log$=relatedreviews&logdbfrom=p ubmed
"TSH determination is diagnostically misleading and only free hormone measurements are reliable for thyroid function assessment."
Guess your doctor hasn't kept up with things.
If you have some labs to share (including ranges), we can help you identify where you might need help. Most people need their FreeT4/T3 levels in the upper half/upper third of the range and, most often, this results in low/below-range TSH.