My experience with these drugs is that their effect is subtle and not cumulative. The directions on Pensaid (that may be a Canadian name) say to apply 40 drops 4x per day. The voltaren gel is more 'gel-like' then the Pensaid. Both feel very cool and dry very fast.
Since you can't take oral NSAIDs (and I assume this is a stomach issue, not an allergy, in which case the Voltaren might be a bad idea) it MIGHT be a way of getting a little bit of relief for a few hours. Based on its OTC status in other countries, my impression is that they're pretty safe.
Hope that helps!