on this page..
http://www.drugs.com/xq/cfm/pageID_1150/int_0/qx/index.htm i searched the basic "metformin", "provera" and "Benedryl Allergy Sinus"....i'm not sure if they are the EXACT ones you're using, so the best bet would be to look it up yourself...here's what it said anyways (for the above drugs..)
You have searched for drug interactions between the following drugs: metformin,Provera,Benedryl Allergy Sinus
Please note: only generic drug names are displayed.
medroxyPROGESTERone (moderate Drug-Food)
Description:
MONITOR:
Grapefruit juice may increase the plasma concentrations of some orally administered drugs that are substrates of the CYP450 3A4 isoenzyme. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. The extent and clinical significance are unknown. Moreover, pharmacokinetic alterations associated with interactions involving grapefruit juice are often subject to a high degree of interpatient variability.
MANAGEMENT:
Patients who regularly consume grapefruits and grapefruit juice should be monitored for adverse effects and altered plasma concentrations of drugs that are metabolized by CYP450 3A4. Grapefruits and grapefruit juice should be avoided if an interaction is suspected. Orange juice is not expected to interact with these drugs.
Please note: only generic drug names are displayed.
medroxyPROGESTERone and metformin (moderate Drug-Drug)
Description:
MONITOR:
The efficacy of oral hypoglycemic agents and insulin may be diminished by certain drugs, including thiazides and other diuretics, corticosteroids, estrogens, progestins, thyroid hormones, human growth hormone, phenothiazines, atypical antipsychotics, sympathomimetic amines, protease inhibitors, phenytoin, clozapine, megestrol, danazol, isoniazid, asparaginase, pegaspargase, diazoxide, as well as pharmacologic dosages of nicotinic acid and adrenocorticotropic agents. These drugs may interfere with blood glucose control because they can cause hyperglycemia, glucose intolerance, new-onset diabetes mellitus, and/or exacerbation of preexisting diabetes.
MANAGEMENT:
Close clinical monitoring of glycemic control is recommended if these drugs are coadministered with antidiabetic agents. Likewise, patients should be observed for hypoglycemia when these drugs are withdrawn from their therapeutic regimen. Dose adjustments of the hypoglycemic agent may be required.
Please note: only generic drug names are displayed.
diphenhydramine-pseudoephedrine and metformin (moderate Drug-Drug)
Description:
MONITOR:
The efficacy of oral hypoglycemic agents and insulin may be diminished by certain drugs, including thiazides and other diuretics, corticosteroids, estrogens, progestins, thyroid hormones, human growth hormone, phenothiazines, atypical antipsychotics, sympathomimetic amines, protease inhibitors, phenytoin, clozapine, megestrol, danazol, isoniazid, asparaginase, pegaspargase, diazoxide, as well as pharmacologic dosages of nicotinic acid and adrenocorticotropic agents. These drugs may interfere with blood glucose control because they can cause hyperglycemia, glucose intolerance, new-onset diabetes mellitus, and/or exacerbation of preexisting diabetes.
MANAGEMENT:
Close clinical monitoring of glycemic control is recommended if these drugs are coadministered with antidiabetic agents. Likewise, patients should be observed for hypoglycemia when these drugs are withdrawn from their therapeutic regimen. Dose adjustments of the hypoglycemic agent may be required.
Met & Benedryl 
