Hi!
It's almost always a bad idea connecting in parallel two diodes (without any compensating resistor or other techniques), to increase their ampacity.
For sure, there will be some mismatches, and one diode will carry more current than the other.
The diode carrying the larger current will eventually heat up and its "equivalent resistance" will decrease. This will end up in a thermal run away, with one diode carrying a current larger than its ratings, with a consequent catastrophic and spectacular failure..
This effect could be mitigated (but not 100% solved!) by:
1) Mounting the diodes on the same heatsink, if possible (still take into consideration the exponential dependence of the current to the temperature, the thermal resitance and thermal capacity, the latter being dangerous during transients).
2) Using a lot of "headroom" (just as an example if you need 2 amps, you might try using 2 diodes with 1.5A ampacity... but at this time a single 2A diode could be cheaper. Still beware of the exponential I-T dependence).
3) Using a resistor in series to each diode (but you'll waste a lot of power).
However, I would never recommend you doing this... I have seen many chinese consumer products failing because of such a poor design practice...
Cheers